But...he doesn't play PT anymore.
I do, but only for certain matchups. I've become more excited about the character lately, though, so, he could very well see more use than he currently does.
B-Air and F-Air have only a slight amount of landing lag. N-Air autocancels after a certain point, I believe. U-Air is fast enough where you shouldn't get landing lag if you aren't using it while falling and right next to the ground, and a full-hop D-Air actually gives you enough time to throw out a second aerial before you land, but, if you don't use them as I described, U-Air and D-Air have a lot of landing lag, yeah.
Squirtle's aerials are rather great overall. U-Air is certainly one of the best in the game--It comboes into itself until high percents, and the entire animation only takes 24 frames, making it excellent for momentum canceling and frame traps on falling characters. F-Air and B-Air are fast, have little lag, and deal decent damage. D-Air pokes shields, has nice knockback, and it sends people outward, making it a nice option for gimps, and, like I said earlier, full-hop immediate D-Air is quite safe due to a potential F-Air/B-Air at the end. Autocancel N-Air allows for a jab to keep yourself safe afterward, and since Squirtle shakes back and forth during the animation, it's hard to tell whether or not he's moving toward you.