Well, the Alpha/XM30 ones are the same: accuracy 4, SS, 6(c). Even though both are on weapons with integral smartgun systems, only the Alpha's does the 4(6) accuracy thing to reflect this, but it could probably be assumed that the XM-30's grenade launcher gets the same bonuses. The AK-98's underbarrel GL is accuracy 3, SS, 6(m).
Like I said, it can be inferred from the price difference between the AK-97 and 98 (950 vs 1250) that the AK's grenade launcher is 300. So, if I'm going to be paying 3200 extra, it had better be using the better stats of the Alpha/XM-30 grenade launcher.
And yes, having one weapon fill the role of 2 is convenient, but 3500 still a pretty steep frakkin price. Like there aren't that many ARs it would be worth it on. Obviously not the AK-97, when you can get the 98 for 300 more. Definitely not the Colt M-23 or the FN HAR, because they're worse assault rifles than the Alpha, and if you can afford the price of one of those plus the underbarrel GL, there is no reason to not get the Alpha which would be at least a thousand cheaper. Same for the HVAR- since 5E doesn't have the special "high velocity weapon" rules, its similarly pointless to get it and a underbarrel GL- it does less damage than an Alpha. Yeah, it has 4 points of recoil compensation, but that's with a shock pad, and it can take no barrel mods, so no gas vents either. Compare that to an Alpha, which has a nebulous "special chamber design" that provides 2 points of recoil comp already, and adding a gas vent 3 and shock pad takes that to 6. The Alpha has 8 less bullets than an HVAR, but otherwise is the superior weapon without the special HV rules giving the HVAR some advantage. So doing the HVAR/underbarrel GL is just throwing your money away. It MIGHT be acceptable on a Raiden for that price.
( I don't count the Optimum, because it already has a built in underbarrel shotgun. There's already another thread going on about what integral means for accessories/mods and whether that underbarrel slot is actually free, so any comments about that should probably be directed there).
Of course, since it goes on any "rifle-sized weapon" or better, it would behoove you to put it on something like an EBR, to widen its already multi-role capability. I guess the price isn't too steep if you put the GL on something like that. Putting it on an LMG/MMG/HMG prevents you from using a gyro mount or tripod, so it might not be wise to use it with those.
All in all, I think it goes perfectly with the EBR, or heck, even an assault cannon, since the GL is not ridiculously more expensive than those. However, even though its like being able to carry an antioch-2 and another weapon at once, I just don't think the price tag is worth it for any of the actual assault rifles since the AK-98 and Alpha are so much cheaper and readily available solutions. You could also put it on a shotgun, but I find it a little ridiculous the "secondary" weapon would cost about thrice the primary in that case.
