I think that trial period is an extremely useful thing especially in reselling hosting business as you are responsible before your clients so making a choice of a provider isn't an easy thing.
I think fasthosts.co.uk is another company offering free trial period, I think this may be a good idea to make a kist of hosting providers offering free trial period.

At the OP:
what type of panel and billing software is offered in HostWW.net plans?