I'm all for concielable droid weaponry. I think it's a nice flavor touch and pretty cool from a narrative standpoint.

I'm all for restrictions though. Having retractable vibroswords would be nearly impossible without oddly large forarms on the droid. Also, I'd probably throw in a setback die or two in combat (a sword sticking straight out of your arm is not nearly as handy in combat as a hand held weapon).

If they went with knives instead, I wouldn't have a problem or add any restrictions.

For blasters, size is again an issue. Having a panel on the forarm that pops up revealing a light blaster is one thing. Having a heavy repeating blaster rifle is another story all together. Also, upgrading such weapons would be nearly impossible. The compartment is built to house the light blaster, so even replacing it with a regular blaster pistol would be tricky. And adding other attachments and upgrades would be difficult or impossible also. This would allow you to add extra costs, difficulty dice, or outright forbid certain upgrades.

Also, keep in mind all the fun stuff you can do to mess with someone. Player throws a despair and now his built in weapon is damaged and you can't just pick up a new one of those at the backwoods street market. Repairing it will be extra challenging due to all the integrated electrical work. Despair! The retraction system for your blades is busted, and you don't have the replacement parts....guess those won't be retracting any time soon. Now the mob boss that's been refusing to let you enter with weapons makes the droid stand outside and you've seriously damaged his level of trust.

I'm not advocating punishing a creative player by any means, but his/her creativity can allow you to come up with some interesting twists.

Basically, the stuff that would be allowed would be stuff a normal player could likely keep hidden anyways. If someone was demanding to make a huge battle droid with a lot of built in weapons, I'd let them, but it wouldn't be conceiled stuff and everybody and their bantha would know the thing is a walking battledroid/tank.

I also have a droid in the party who wanted to integrate a mechanics toolkit into his body. I let him spend the credits for it and a backpack, viola! integrated tool kit. No mechanical bonus, no penalty, just flavor.

Same for the claws. Retractable they may be, but as long as he isn't expecting any sort of bonus/penalty to hiding them, outside of those already mentioned, I see no problem with them.

I also have a droid in the party who wanted to integrate a mechanics toolkit into his body. I let him spend the credits for it and a backpack, viola! integrated tool kit. No mechanical bonus, no penalty, just flavor.

Same for the claws. Retractable they may be, but as long as he isn't expecting any sort of bonus/penalty to hiding them, outside of those already mentioned, I see no problem with them.

R2-D2 has a built in mechanics toolkit, so that's pretty solid for canon. He also has a taser, a saw, and a fire extinguisher in his trash can body. His penalties are that he's a trash can and wouldn't be able to use any of this stuff otherwise.

I think the fact that for 35 credits anyone can just walk up, affix a bolt, and take total control of you is a fair enough balance point.