Costar takes 5 minutes max to do. I'm more scare to remove caps from a PCB mount board since I always snag the switch
This. I was so scared of ripping out the switches when I first removed the key caps on my 11900, but I think I've got the hang of it now.
I've only had experience with Cherry PCB Mount and Costar stabilisers, but Costar feels better to me. I feel that Cherry PCB Mount stabilisers somewhat dampen the keys, which I guess some may like.
Concerning the fit, sellotape takes care of that and it's not like you'd be changing caps that often anyway, so that's not really a deciding factor to me.
Edit: Interesting contrast with shibby's post above, haha. I guess it really is personal preference as to whether you like the "mushy" or "clinky" sound/feel.