[Tassyr]

So aside from the fact that the external smartgun system requires a mod slot on top or bottom... is there any other disadvantage to it?
I'm trying to find out why I would pay, in the case of a large gun, up to two or three times the cost of an external smartgun system...

[Emil_Barr]

Related Question: 4th and 5th edition

Can a pistol with an external smartgun system fit into a concealable (or for that matter, regular) holster?

[Tassyr]

I didn't see anything saying [SR4] it CAN'T, but considering you're adding a camera mount to the thing I'd assume it'd be tricky. That's just me though...

[ZeConster]

A smartgun system only includes a capacity-1 camera, though, so it's essentially a micro-camera. If I were to guess, I'd put an external smartgun system at between -4 and -2 Concealability, so I don't think it'd make the weapon too bulky for the holster.

[Mantis]

You could apply those sort of penalties but why bother? None of the other accessories apply any kind of modifier to concealability so why pick out external smartguns? I assume that if they can jam an internal smartgun into a pistol as a retrofit then the external one they slap on top can't be all that big.
Tassyr, for the larger guns the only reason you would want to put in an internal smartgun is because you want that  mount for something else, like a scope or something. At least that is the only RAW mechanical reason for it. Other GMs may do things like say that you can't get the Improved Rangefinder mod unless the smartgun is internal or have you worry about things being jostled or knocked off it is external.