Sounds good for the money 'cos £450 gets you a Garmin with a 5.5" screen on the 182. http://www.garmin.com/products/gpsmap182/spec.html
I guess that the acid test is "does it do everything you want it to?" and if the answer is yes, then it's cheque book out time.
The only other thing is the fact that there's a shrinking margin between B&W and colour plotters. I reckon B&W won't be around for much longer and the price of colour units will come down again. If your new RIB isn't going to be ready for a while, why not wait until launch-time before commiting to all the accessories?