They will do the job well - possibly too well (mine can be far too hot in even a Scottish Summer). They will restrict movement to some extent, but shouldn't be too bad. Beware that they work to buoyancy aid standards so won't turn you the right way up on their own, and even if you combine with a standard 150N jacket they may not work properly (to be sure you need 275N).
Also beware that if you buy a two piece and just have the trousers on and go for a swim you will effectively be being supported by the legs (i.e. head down