Sherpadesk is pretty user friendly because it is very simple to use. However, it might be a little too simplistic, as it cannot do many advanced functions. If you're looking for just a quick way to log and track tickets, it does the trick. However, if you want something really robust with a lot of CRM-like features, you won't find it here.
Mobile site does not work very well, as fields and things are not fully accessible on a mobile device. You can separate things into queues, but that is not always robust enough when farming data on like issues.