The owner of SMC said a slight puff is not that bad as long as it is soft and not rock hard. Also said shorty packs are more prone to puffing due to so much material being stuffed into a small case. All of my packs which include SMC, Trinity, Reedy, Speed zone, Peak/Orion all have some puff but all work and balance fine. I throw them out when the case starts to open or they really bow.
As a side note my 5 Thunder power packs are perfect as the day I bought them charging at 20 amps on a thunder power charger. Also had really old Orion/Kokam packs plugged in to my starter box for 3 years in my garage that still worked and were balance and a 8.15 volts, which is pretty amazing. Really seems like every company is selling the same Chinese junk so don't over pay thinking any company is making a better product, very few are.