Having just recently acquired a G29.4 to go with my G20.4, I can say this:
I like the small size of the G29 when it comes to carry. But it comes with significant compromises.
Assuming you're familiar with other Glock models, which would you rather shoot, and which would you rather carry, a G17 or a G26? That really is very close to the comparison. The G29 is actually between the G19 and G26 in size, but there's no illusion about the grip space, if you want the pinky on something you will need to add that to the magazine because it's not on the frame.
Velocity reduction based on my loads is somewhere around 55fps going from the G20 to the G29 with a 180gr bullet. Is that enough to matter to you? A reduction in velocity does mean a reduction in recoil, which on a smaller lighter gun, I feel balances out pretty well. Though that is subjective, I suppose a person could run the number through a recoil impulse calculator.
Weight between the two is something I have not checked. But just by feel there is an obvious difference, though I suspect 5 additional rounds of 10mm probably make up about the same difference as the weight between one gun and another without magazines.
The primary reason I have this new G29 is not because I can't conceal the G20 through the summer using, an appropriate holster with reasonable forward cant, and an appropriate cover garment. I bought it because sometimes I just don't want to try that hard, and I don't want to carry that much weight. Sometimes I'm willing to take a reduced sight radius, smaller grip, lower capacity, and reduced velocity, in exchange for convenience and comfort. A hot summer day is certainly one of those times. Higher altitude hikes would be another.
A worthwhile consideration is that you can get a longer barrel for the G29* and magazine extensions, which will bring it closer to the size of the G20. You cannot make the G20 any smaller without chopping it.
*KKM will cut a custom length barrel at no extra charge, up to a certain length. For the G29 I am fairly sure they will go to at least 4.25", if not 4.5"