If they fit good, making good contact and unlikely to accidentally come off, then they should work fine. I mean that there are standards, and then there is reality. In very high current apps, you wouldn't want to go from a larger terminal size to a smaller one but you're doing the opposite.
What you linked are just inline adapters. There is no soldering or crimping involved. If you instead wanted to replace the one on the end of the existing UPS cable, then you would want a high quality crimp tool and crimp type connectors. Trying to use a low quality crimp tool, let alone pliers, probably won't work out well because that's a somewhat high current (dozens of amps) connection for that 1350VA rated UPS, but it's a non-issue if using what you linked.
Cheaper, sure, if you have a few hours to look and are savvy at browsing Alixpress, you could probably get a 20 pack or more for a dollar or two (whether the quality is worse, I couldn't say till I had both in-hand to examine. The ebay sellers may also be shopping at their lowest cost chinese supplier sites), or cheaper still would be to file down the terminals on the battery to the smaller size (voiding any warranty if there is one on the batteries), but what you linked seems like the most time effective way to solve this without resorting to that at only ~$8 delivered for 4 of them.
One last detail though - they are described as tin plated but not tin plated what. Better quality usually have brass as the base metal instead of steel. You could ask the seller...
Also is there room in the battery bay without having to resort to bending them? Bending can have an unpredictable result, how well it all fits together and maintains optimal low-resistance contact.
