hi,
Version 5.5 is currently in Beta testing phase, you can try it out through our demo.
As for SDK based apps, you will at the very least have to recompile them but might have to modify them if/when you upgrade to 5.5 it is hard to tell in advance.
Finally, Checkmate 5.5 is web server based so you can either use our MyGeotab hosted solution or you can host your own Checkmate web server and the users would connect via Internet Explorer (
http://servername/).