I switched from ADSL2+ to SuperFast Basic FTTC on 15/9, and it was so much easier than I expected. I had some trouble configuring IPv6, because TP-Link had sent me more complicated instructions than I needed - another IDNetter sorted it out for me some days later, and not having it didn't prevent my having a connection. I immediately got download speeds of 36 and upload of 10 on my ethernet-connected desktop. The only surprise was slow(er) wifi - the first time I did a speed test on my laptop, I got 35, but a short time after that it was only 5 and stayed like that for days. My Amazon Firestick also dropped to 2, even though it got 5 or 6 on ADSL. I phoned the computer place that takes care of us to see if an engineer could sort it out, but when he found out the switch had only taken place 3 days earlier, he told me it would be premature. Apparently it can take 10-14 days for wifi to settle down, which really surprised me. Yesterday, I checked my laptop and the download speeds were back up to 35-36, and my phone was just over 20. The iPad is still slow and the Firestick hasn't improved (ironically, the main reason I wanted the higher speeds), but I'm hopeful they'll eventually improve too. Good luck!
A bit later: laptop back down to 5! So wifi still very variable.