I've owned both,
1) the model 30 glock (that holds 10 rounds and is compact)
BTW, the glock model 36 is compact and only holds 6 rounds and the SLIDE is the same thickness (width) so you are NOT gaining anything for CCW.
2) and the full sized FNX-45 that holds 15 rounds + 1 up the spout.
I bought my FNX as a back up.
I currently carry a full sized Kimber Polymer TArget that holds 14 + 1.
The secret to being able to carry it comfortably is to have a good holster (I have a comp-tac "c-tac" inside the waist band kydex) and a SUPER GOOD GUN BELT. The belt MUST be 1-1/2 inches wide and it MUST be 1/4 inch THICK. I had a nice high quality leather belt that was 1-1/2 x only 1/8 thick and the gun/holster MOVED around all the time and would rub you raw! (so then you leave it at home or carry something SMALLER that is LESS Effective!)
I just ordered the super tuck DELUXE from crossbread holsters
for the FNX.
I bought the FNX in case my KIMBER dies (it is 12 years old) and I can no longer buy parts etc as Kimber no longer makes this weapon. (that's why the FNX is a "back up". When the kimber fails, the FNX will become my ccw)
The advantage and disadvantages as I see them:
Glock.... it's smaller, therefore easier to conceal
FNX..... holds 5 more bullets.
FNX..... easier to take down . They come apart very similar, but on the glock you have to pull down on the two little slides on the side while holding the slide back 1/8 of an inch. This is not always easy! (wait till you get old and get arthritis). The FNX you lock the slide back, turn a lever, and move the slide off the weapon. The recoil spring looks to be the same design.
FNX.... since it is larger, it has a longer sight radius and the barrel is longer.
Glock.... is about $550 -$600
FNX..... is about $799 but comes with THREE 15 round mags.
GLOCK and FNX mags are very close in price.... $49 to $42 bucks each.