Burst vs Flex: HSA/FSA for Your Business, Compared
Burst vs Flex for merchants: a 30-minute self-serve setup vs a checkout integration. Compare pricing, recurring billing, and who can offer each.
6 minute read
TLDR;
For a merchant, Burst vs Flex is a choice between adding a benefit and building an integration. Flex (withflex.com) puts HSA/FSA card acceptance inside your checkout, which means integrating their payment rails into your stack, on terms you learn through their sales process, in a model built for online merchants. Burst adds HSA/FSA savings to your business without touching your checkout at all: self-serve signup, live in about 30 minutes, $100 a month with no contract and never a percentage of your revenue, and it works identically for online, in-person, and membership businesses. Your customers pay you the way they always have; Burst handles the letters and the reimbursement, and guarantees the member a refund if a letter isn't issued or a claim is denied.
(Shopping as a consumer, not a merchant? You can get a letter for any purchase directly from Burst.)
Burst vs Flex for merchants
Burst | Flex | |
|---|---|---|
What it is | LMN and reimbursement platform, no checkout involvement | HSA/FSA card payment infrastructure in your checkout |
Getting live | Self-serve, about 30 minutes | Checkout integration on their rails, typically weeks |
Engineering required | None; checkout, POS, and billing untouched | Yes; their checkout in your stack |
Merchant pricing | $100/month, month to month, no contract, no revenue share | Not public; learned through their sales process |
Built for | Every business: retail, gyms, spas, studios, online or in person | Online merchants running their checkout |
Recurring billing | Your existing billing, untouched; no card rails | Limited support |
Member cost | $20 one-time letter fee, member or merchant pays | $15 LMN where offered, on their rails so additional fees apply to your customers |
Customer protection | Automatic refund if no letter is issued or the claim is denied | None advertised |
What Flex is for a merchant
Flex is a payments company (Y Combinator S23) whose checkout lets your customers pay with HSA/FSA cards, substantiated in real time, split carts handled, subscriptions re-validated at every renewal per their documentation. Equinox is the flagship partner, which tells you who the model courts. It's real infrastructure, and it costs what infrastructure costs: an integration project, their rails under your revenue, and commercial terms that aren't published anywhere you can read before entering the pipeline.
What Burst is for a merchant
Burst adds the HSA/FSA benefit without becoming part of your payment stack. Signup is self-serve and takes about 30 minutes; nothing changes in how customers pay you. Burst runs the Letter of Medical Necessity side with licensed clinicians (letters within 24 hours of approval), and Burst files the reimbursement claim for the member; their plan administrator pays the reimbursement out of their FSA, HSA, or HRA to them.
Pricing is public: $100 a month, month to month, no contract, never a percentage of your revenue. Members pay a $20 one-time letter fee unless you cover it. And the offer carries a guarantee Flex doesn't advertise: if a clinician doesn't approve a letter or a claim is denied, the fee refunds automatically, so recommending Burst never costs your customer anything.
The differences that matter
Integration project vs 30 minutes
Offering Flex is an engineering decision with a sales process in front of it. Offering Burst is an account signup. If you have a developer, a roadmap slot, and patience, the first is possible; if you want the benefit live today, only Burst can offer that.
Who can even use it
Flex presumes an online checkout to integrate into. A front-desk gym, a med spa, a studio on custom billing, a farmers-market retailer: outside the model entirely. Burst assumes nothing about how you get paid, so every business type onboards the same way.
Whose rails your revenue runs on
With Flex, HSA/FSA purchases and renewals flow across their card rails with real-time substantiation, because IRS rules (IIAS, Notices 2006-69 and 2007-2) demand it for card payments. With Burst there are no card rails in the loop at all: members pay through your existing billing, and the letter plus their plan's rules covers the expense. Nothing new in your payment path means nothing new that can fail in it.
Terms you can read
Burst's pricing is published and flat. Flex's merchant terms come through their sales process. One decision you can budget today; the other starts with a demo call.
When Flex makes sense
You're an online merchant that specifically wants HSA/FSA cards accepted inside the checkout itself, at a scale that justifies an integration on their rails, and you have weeks to build the integration.
When Burst makes sense
Every use case: in-person, online, and hybrid businesses, membership billing, owners who want it live this week, and anyone who wants to know the price before the pitch. See how it works or go live now.
Frequently asked questions
What does Flex cost a merchant compared to Burst?
Flex doesn't publish merchant pricing; terms come through their sales process (typically a rev share %). Burst publishes everything: $100 a month, month to month, no contract, no percentage of revenue, plus a $20 one-time member letter fee that you or the member covers.
Do I need a developer to offer Burst?
No. There's no technical integration; your checkout, POS, and billing stay exactly as they are. Partners are live in 30 minutes.
Can a brick-and-mortar business offer Flex?
Flex is built around online checkout integration. If your revenue happens in person or through your own billing system, you're outside their core model. Burst works the same for online, in-person, and hybrid businesses.
How does recurring membership billing work with each?
On Flex's rails, each renewal is re-validated in real time per their documentation, because IRS rules require substantiation of HSA/FSA card charges. With Burst, members keep paying dues through your existing billing on their normal card, nothing changes in your process at all, Burst handles everything else.
Can members get letters for past purchases?
No. IRS rules require the letter to be dated on or before the purchase. That binds Burst, Flex, and every other provider equally.
Related guides
Offer HSA/FSA savings this week
Self-serve setup in about 30 minutes. $100 a month, no contract, no revenue share, no integration. Get started with Burst or see how it works.
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