If close to equal means the cells are within 50mV or lower from each other that's fine..
4170mV
4180mV
4130mv
If it's getting up higher than that between cells, within 100mV or more, then something is going bad, and much past that isn't good for it at all.
4170mV
4180mv
4070mv <- iffy cell
A little bit of puffiness and LiPo can go hand in hand, a little bit. Swollen is a different story though.
If it's been dropped, stored fully charged or almost dead for an extended period, then you may want to start looking for another battery as it could be the beginning of the end for it. Also if you notice the run time of that battery is diminished over your other one then it's on the way out. They can also just fail from being a complex chemical mess that's mass produced and only a few out of thousands in a run may get tested out.
If everything is checking out good for now, keep a closer eye on it, and when not being used for an extended period stored in a cool, dry place at 30%-40% charge in something that can't catch on fire, but is vented. That goes for all your P2 batteries really. You don't want to go opening up any sealed container that has had one of those things go bad inside of it, if you'd even get the chance too. You also don't want to go running your P2 with one of those things if it's on it's way out, especially if you're flying somewhere that recovery isn't an easy option, e.g. over water.
