The case in favour is strongest above a certain price point. For a purchase somebody would hesitate over, splitting it into instalments removes the hesitation, and the provider pays you in full immediately while carrying the collection risk themselves. You are not extending credit and you are not chasing anybody. For higher value goods and services this frequently pays for itself, because the alternative is not a cheaper sale, it is no sale.
The case against is arithmetic. Fees typically run several times a standard card rate. On a low value item with a thin margin, that difference can consume most of what you were making, and the conversion lift has to be substantial to compensate. Run the calculation on your actual numbers before adding it: take your margin on a typical order, subtract the additional fee, and work out what increase in orders would be needed to break even. Sometimes the answer is obvious in either direction.
There are two second order effects worth knowing. Deferred payment tends to increase returns, because the psychological commitment at purchase is smaller, and a return on a split payment is administratively messier than one on a card. And these providers have attracted regulatory attention in several jurisdictions, with disclosure requirements tightening, so the terms you agree to today may not be the terms in two years.
The reasonable position for most first year businesses is to wait. Add it when you have evidence that price is the objection stopping sales, rather than adding it because competitors display the badge. If you do add it, watch your return rate for the following quarter, because that is where the cost hides.
Check what it does to your customer support burden before committing, because payment questions arrive at you rather than at the provider. Somebody whose instalment failed, who wants to change a payment date, or who is confused about what they owe will contact the business they bought from. That is a support cost that does not appear in the fee, and it is worth understanding what the provider handles and what falls to you.
Watch the effect on average order value honestly, since the increase is real and it is not free. Customers buying more because payment is deferred are also the customers most likely to return items or to dispute charges later, and a rise in order size that arrives with a rise in returns is a smaller gain than it appears. Track both together for a quarter before concluding it worked.