It's an EXCELLENT tool for your tool box if you want to move away from virtual complete dependency on a mechanic. And is useful even if you are (initially) a novice but want to learn.

I've got an HP2 Enduro and I do all my own maintenance: complete to strip down to engine to re-coat frame when I changed clutch.

So maybe I'm at the extreme end, but if you have at least a critical set of tools, and can read, you can do a lot of your own preventative maintenance. BMW has a very good CD-based maintenance manual for all the later model GS's. It's based on what the dealer uses. You can use common senses and tools like the GS-911 to trouble shoot issues and decide if you feel comfortable fixing them, or need more expert help.

If your bike is off the warranty, there's no real down side to doing your own services, as long as you use your head to read what's in the manual and take your time.

Don't buy a GS-911 from the Far-East: it's going to be a clone. The real benefit of the GS-911 is the support you get from the developers and the very active forum they run. It doesn't make sense to have a bike that's worth more than some people's houses, and try to save £100-£200 on a really useful tool with good support.

How much does your helmet cost? Or your sunglasses? Do you buy brand name oil, or the cheapest that you can get on eBay?

I was having a problem on a trip, and in the middle of Kenya a guy in Argentina on the GS-911 forum told me he thought the reason my bike was sounding like a Harley with a stutter was because one of my throttle cables was caught up. He said he'd had same issue, and found a pebble stuck in the linkage.... hmmmm I thought. Well let me try....pink!!!! Dang. Problem solved.

Buy it. And remember, if all else fails RTFM (Read The %u%%ing Manual). But seriously RTFM.