I also ordered their free sim and it arrived very quickly (after some emailing back and forth as to whether they would send it to Canada (they did) and if it would be okay not to activate it until I got to the UK later this year (it is).
As I mentioned in the earlier thread to which you've alluded, I'm a bit concerned about the information they ask for going to third party advertisers when you activate online, but I'm wondering from the insert included when the sim arrived, if you could just insert the sim and purchase a topup card at a retailer instead of online to buy credits, and then use the sim itself with the topup credit to complete the activation without going further. Let us know on here how the activation goes for you (online activation or just put in the credits from a topup card or voucher from a retailer and if that's all that is needed), and if you're satisfied with the call quality and service.
Thanks,
bj-21.