True, but 18650's are somewhat notorious for being dubiously specified in the budget price range since they are essentially the "AA" battery of lithium chemistries and there's no mention of chemistries in the OP's link. In fact, the Samsung battery mentioned is regular Li and is brilliant for rebuilding power tool packs. If you're after LFP, first check is to make sure they're 3.2 VDC and not 3.7VDC when charged, I guess.18650 is a case size, not a chemistry.
The problems I've seen in series / parallel setups have been related to the weak cells in the parallel strings getting stressed and hot. BMS's I've looked at monitor the parallel strings as if they were single cells. That is simple but not ideal.
If you buy batteries already fitted with spot welded nickel tabs they are ridiculously easy to solder together.