I hate to sound real negative, but good luck trying to find a firefly bucking. I haven't seen one of those in stock for almost two years. Both Benshee and Bash have used 'promy' buckings with good results. Just be sure to get the 'soft' version because the 'hard' ones are trash. If I ever use a regular bucking and not r-hop, my favorite is the G&G green bucking. It's been the best bucking for all types of guns, FPS, and varying weather conditions I've used so far. Both Benshee and Bash were starting to convert their guns over to the G&G buckings versus the promy due to the better performance and cheaper price tag, but then we started getting on the r-hop band wagon and well, the rest is history.
If you prefer the 2g buckings, I've got a one or more just laying around that are still in the packaging from my former misguided KWA AEG fan days. If you'd like to purchase what I've got, just PM me.