With IXL, you can practice up to 10 question for free without subscribing, since you already do mathsfactor.
Ixl doesn't teach, though if you make a mistake, it will explain the method and how to get the answer.
They have feed back system but I don't look at it, so not sure if any good.
If you subscribe, you get access to whole content, from reception to yr13. It's £69 for maths, £99 for both maths and English. You can subscribe monthly as well.
Also you can use part of [[https://www.mangahigh.com/en-gb/
mangahigh]] for free, though access is limited. Their games are fun.
[[http://khanacademy.org/ Khan academy]] is free, but it's us site, so money question is no good. Its contents are great, including maths, science, history, programming, grammar, etc. Feed back system is great too.
Mathletics' contents are good too, but I have no idea how it works since my ds get it through school.
There are sumdogs, komodo maths, etc which was recommended by other posters before, but I have no idea.