I wasn't impressed with the Buildtak (or Im probably not used to it...), and since I use PEI on my other printers, I managed to get hold of 400x400mm PEI Sheets, and I installed it yesterday!
https://www.youtube.com/watch?v=zVLsKjvT5zI
https://www.youtube.com/watch?v=zVLsKjvT5zI