If you have a coach ( I assume a real person), for Crossfit, then one can assume your level of fitness is above what the band is designed for. You might be better looking at a Polar RCX5, HRM, GPS module - or any other similar system.
Working out your goal is 1st priority.... to get fitter, enter competitions (and get better results), lose weight, increase cardiovascular.....?
Once you know your goal, get a monitoring system that works best for that sport. For example, not much point using the Band for Triathlons - battery doesn't last long enough (using GPS) and it's not waterproof!
For Crossfit - I would recommend a system with Chest HRM. Wrist worn ones will hinder you doing Crossfit.