I've done it a couple times now. The street camber plate super simple. The sleeve over kit is more involved. They're both relatively simple but it will be time consuming your first time around if you take it on yourself. I think my DIY guide is pretty thorough and I'd be happy to help. I have to reiterate that I have no formal training though. LOL
The money you save could buy you some setup tools. Something I've been threatening to buy myself. Then you'll never have to go to a shop to change your setup for track or street. As is, you need to adjust the toe any time you change camber very much and you can't just change the camber by the marks on the camber plate alone.
I think the GC stuff is good quality for the price point. I'd probably avoid the low profile camber plate kit considering the recent QC issues. The regular kit and sleeve over kit don't have that same welded bolt.
If you're going to a shop, I think you should use a shop with a lot of experience with the E90. Unfortunately I don't know which shop that is.
I think Bimmerhaus is a pretty good shop, all things considered. I had a somewhat negative experience when I had them do the alignment to my car after installing the sleeve over kit then I found out the hard way that you can't just tilt the shocks in before going to the track without adjusting the toe. I corded the inside of my tires after the first track day with the sleeve kit. I'm somewhat lucky I didn't have a blowout mid corner at the track.
When I had the alignment done, I asked if I could just tilt the shocks in before going to the track. They said go for it and they gave me no warning that the toe would be affected. Maybe they didn't know the tow would change or just forgot to tell me. I don't know. In the end it's my fault for not being more familiar with the suspension but it kinda felt like they let me hang myself.
I play real sports. Not tryin' to be the best at exercising. - Kenny Powers