well if you look to forum you will see there is also many people who have very bad experience with some developers so if you had no problems it doesnt mean everybody feel same like you. Also by allowing trials it help people see themselve if product is not interferring with some other 3rd party product on their site which is very important - you cant test that on develůoper demosite. Also some developers tune product on their demosites so after you install it on your own site it doesnt lookm or see more work exactly same as on developer demo site ...