Polymer is hard, rubber is soft. I have the Crimson Trace 305 and 405 grips on different J frames - both are rubber, both have a cushion (of sorts) over the backstrap. I believe the polymer laser grips do not cover the backstrap, so are probably no more comfortable to shoot than the standrd boot grips that come with most of the J frames today.
I find J frames uncomfortable to shoot for more than a few shots with their "standard" grips, either the Spiegel-type boot grips seen today or the Magna (service) grips they used to come with. While it's conventional wisdom that most social encounters which need a gun tend not to involve high round counts, I like to practice with what I carry and need some padding to do much J frame shooting (with 38 Specials - I've discovered the joys of the 32 H&R Mag in a J frame, which is a completely different experience, but that's for another thread.)
Lasers are an absolutely magical experience once they're adjusted for your ammo and grip/trigger pull technique - a hole appears exactly where that dot was at the time the hammer fell, and you can have that precision shooting the gun from the hip or any other location. You don't have to bring it up to eye level to aim accurately. And you don't have to align anything - just put that dot where you want a bullet hole and work the trigger.
The 405 is a "boot grip" size, that only comes down to the bottom of the grip frame. I have average size hands, and my pinky finger ends up under the bottom of the grip. I can deal with that when shooting, but the 405 grip is fairly narrow, which along with the short length makes it easy to conceal in a pants pocket. But despite the bit of cushioning over the backstrap, I don't find it particularly comfortable to shoot. It's better than the regular grips, but not a lot. The 305 has a longer grip with room for all of my fingers, and it has more cushion over the backstrap, so I find it more comfortable to shoot for longer periods. But it's a bit big to fit in one of my pants pockets. (I carry that gun in a holster almost all the time, so it's not an issue for me.)
Both of my laser grips have red lasers, as greens weren't available when I bought 'em. But red lasers become less visible as the light level goes up, and while defensive uses of guns are reported to occur mostly in lower light situations, the issue of practice is still there. The range I'm a member of is all outdoors, and we can't shoot after official sundown (when it's still pretty bright) so I don't get a lot of useful practice with mine unless I go to an indoor range. (Occasionally it's cloudy enough that I can see the red dot at 5-7 yards outdoors, but it's not that common.)
Having fired a friend's gun with a green laser in bright daylight I would absolutely choose green over red if I were doing it again. That green dot was instantly visible as far as 15 yards out. That was as far as we set up targets, but I suspect it would have been visible even farther out.
BTW, apart from shooting convenience and accuracy, lasers are one of the best training device imaginible for a J frame. I leave the ammo in another room, load up with snap caps, and spend time dry firing at the corners of picture frames or spines of individual books across the room. You may be shocked to see how much that laser dot jumps around the first time you try it, but the instant feedback lets you tighten up your grip and smooth out your trigger pull (if need be) until you get rock solid letoffs.
