If anyone has experience of them them I think it is fine to reply about specific companies by pm ( private message facility). Of course, you will have to judge for yourself if you think the reply is genuine.
I used one of the Birmingham - based online providers for DS1 in the last 2 months before the exam. This was partly because DS had become quite bored with the papers and it was a way to keep him going and partly due to the fact that he hadn't done particularly well in the company's mock exam and they gave the impression that they had such a great solution with the online testing. I think it was ok in that it was a welcome change for DS and working on a computer always seems more fun (it gets marked without you to
) but on the whole it wasn't that impressive: the maths day questions were good, the NVR is ok too, but the English is weak and unspecific, the VR is irrelevant to the consortium exams (although HGS did have a VR paper at the time) and the day for times table challenge was a nice gimmick but a waste of money. However, I did change the plan so that he only did maths and NVR work and they were professional to deal with.
I think the problem with most tuition - online and otherwise- is that they are often confident with maths but quite uninspiring when it comes to the English work.
With DS2 I tried the Bond online practice tests for a short time. They were cheaper and provided plenty of material with specific questions on particular areas but the level of difficulty didn't seem to be graded as the papers are. I would guess that they are at the 10-11 years stage with some 9-10 years questions(?).
Online providers are good to dip into but are limited as a long-term structure, although I have read of people on here saying that they used them quite extensively. I guess it depends on your child's needs.