Its a good rating to have if its the only IR rating you can afford time/money wise.
If you have the time then get yourself an FAA IR, you will cover a lot more flying in a lot of detail and its a damn good grounding for building upon later. The other good points to remember are that
- Upon passing you get an IMC on your UK licence for free anyway!(Bar the CAAs £64 fee!)
- The IR is for life and as long you shoot the approaches, etc it self certifying.
- You therefore dont need to keep renewing your IMC as it based on your FAA IR so its cheaper and less hassle.
I went over to California and did mine as a holiday rather than sitting on a beach, I spent about 60 hours flying round as combined it with touring a bit of the US which if you talk to the instructors most are more than happy to do.