As a reseller of touchscreens, Clevertouch are the market leader whilst Genee have a tiny part of the market, hence why they need to offer attractive warranties etc. As mentioned by others you should be able to get a loan unit to trial, i know Clevertouch offer this service. Feel free to DM if you require any assistance with this.
Alternatively the Promethean Activpanel is quite cost effective.
The main differences between the screens is the software used to drive them and ability to interact with existing lesson plans (notebook and Promethean for example). Make sure the software meets your needs as much as the screen itself.
Happy shopping :-)