I tried some subscription websites in the past and concluded they were a waste of money as they didn't really suit my DCs and we always went back to books. I never heard of the website you've mentioned, but £130 seems like way too much and why would they want you to pay or a 7 years membership in advance?
Personally, I would not go for it, but having looked at their website, they some free resources to download as well as a 14-day trial period for just £1.97. If I were you, I would get all the free materials first and see how good they are and then go for the trial period and based on that, you would have a good idea of whether what they offer would be suitable for your DCs.
I have found the website below very good - loads of free, printable maths work sheets (and answers, too) which can be searched by topic, so very easy to find what you need. I think they are based in Canada, but it never made any difference to us. There is no need to subscribe, just go on the website, find what you need and print it out. http://www.math-drills.com/