Rose/feathertail bettas have a lot of tail space or whatever they're called. Just that the tail mass is larger than other fish. The tail rays may snap from the weight of the tail or the fish may succumb to biting off as much as it can to lessen the weight of its tail, or not swim around much so they don't have to deal with the weight. They are also more prone to swim bladder and other diseases because of extensive breeding- they are bred for mostly form and look only, so the weak-bladdered, easy sick ones' genes probably get passed on (well I'm inference-ing here so feel free to correct me). Think of it like this- you are forced to carry around an extra-heavy suitcase for the rest of your life. You'd want to lessen as much weight as possible so you wouldn't have to drag it around.
I've heard somewhere on this forum that you should flare a rose tail or feather tail several times a day as so to strengthen their tail muscles. I may be wrong, though.
In my opinion, you should go for the comfort of your pet instead of the look.
Hope this helped.
Sergio- Green-blue metallic HM. Red/white/green fins and green iridescence.
Comet- Silver-blue metallic HMPK piebald dragonscale. Red/silver-blue/black/??? fins.
Neptune- Koi/marble delta tail.Translucent fins dappled with orange and black. You'll be missed.
Indigo- Purple veiltail. Purple fins with some red and white at the tips. S.I.P., buddy.