The main thing your after is the certificate that comes with it and proof its fitted (garage reciept). Thats what my ins company requested when i restricted my drz years ago. Im sure iv seen replacement certificates on ebay, just a garage reciept you will need.
Definitely no need for a certificate at all. I used to sell them. In the event of an accident the onus is on the insurance company to prove you weren't restricted as long as you are you're fine.
As long as the bike is 33bhp or less (at the rear wheel) you don't need anything. Some insurers ask for proof, but the certificates etc. don't mean anything in law. Its up to the police to prove you are doing something illegal, so if they for e.g. see you doing 120mph on your GSXR they are going to seize and dyno it.
If you do want something to wave at them a dyno chart is best as it serves the helpful double purpose of showing you your fueling and engine condition etc.
If a particular insurer gives you a hard time for not having proof try another, i was not asked at all by the insurer i used while restricted (it was bikesure i think, may have been carol nash)
Something as simple as a homemade throttle stop is totally legal as long as it stops you getting over 33bhp.
the good news is that BMW made their own 33bhp restrictor kit, or rather a throttle stop. so if you phone up your local bmw parts place they should be able to order you one.
Seen this confirmed in a couple of places through a google search, apparently it costs about £35 (not fitted obviously)
if i were you i would get that, fit it yourself and keep the receipt handy to show if the police that ask for it (very unlikley)
its lucky as most bikes need inlet rubber washers that are a bit of a faff if you arent used to working on carbs etc. also the company that makes them FI international is the same bunch of thieves that are talked about in JT's link
-- Edited by Albert on Monday 2nd of June 2014 07:47:26 PM
I have one for a BMW gs850, it plugs in to the 'fuse box" and advances the timing thereby dropping the power. it is bmw tyco v23134-z1015 6136-8366621 2 pin diode, if it fits you can bung me something for it.