With the old Uneo we did a lot of very good work. For drilling 8mm through bolts I cannot imagine anything better. With a bit of forcing you can get an Uneo into a standard 6 L Daren drum, and then store the metalwork and batteries alongside. Under a kg and with a light hammer action, I found I could place bolts at full extension one-handed. Unfortunately, since 2011 all of our Uneos have slowly died. Certainly they are not as rugged as a full-blown commercial SDS-plus drill, such as the (identical voltage) Makitas we now mainly use. But I have to use two hands to place a bolt with the Makitas.
One of our club members ('potholer' on here) took one of the dead-electronics Uneos and replaced the electronics with a much simplified mechanism. Unfortunately, upon the last reassembly of the case, a wire ripped out of the reversal switch, so it needs some more fettling.
I never tried bolting with the built in battery, I would guess from the capacity you might get 4-5 8 mm through bolts, which would perhaps suffice.
I'm not sure if I ever wrote any explicit instructions for the Uneo. A major issue is that when you open up the Uneo, the gear box comes apart as well, and you have to seat it all back together in one. This involves pulling the chuck forwards, and constructing the pneumatic section in the correct order.
Here's a photo showing a Makita and an Uneo open at the same time - full size Makitas are much easier to work on:
https://migovec.files.wordpress.com/2011/06/img_0005-scaled-1000.jpg
Also my most watched video on Youtube (!) is one of the working mechanism with the case open, which might be useful when reconstructing.
https://www.youtube.com/watch?v=JK0H3pblEt4