i need a gps for trail bike use??

as the header says.... needs to be mobile and small..colour screen would be nice but not essential, dont need a phone built in. but it definately needs to be able to take the ordinance survey landranger downloads and to display them properly.this will be fitted to a motorbike so a quick release bracket would be nice, and also in the car occasionally..so ...has any body any opinions or recommendations for me to examine.
i wpould appreciate any feedback on this subject including any model to stay well clear of.

thanks

steve