I had to use this service (in West Sussex) about a month ago to see a consultant.
My GP gave me a choice of hospitals and dates. I chose the one best for me and toddled off armed with a URL, a booking reference and a PIN.
Next day I made the appointment online without problem (although the waiting time was nearer 4 weeks rather than the 10 days hinted at by my GP).
A couple of weeks later, written confirmation arrived from the hospital.
Last week I duly turned up at the hospital on the appointed day and time and, lo and behold, they were expecting me.
The system worked OK for me. ;-))