I've only used the X7 about five times, and four out of five the loadings have been excellent. The first time was the full route, Sunderland to Stockton, and it was average from Sunderland to Seaham, and then relatively busy to Wingate, but quietened down to Middlesbrough. Other times have been from Sunderland to Peterlee, and have had excellent loads.The first few time I used which was the week it launched it had very few passengers, although the weather was awful that day. The second time I rode it from Sunderland to Stockton it was okay but not spectacular and was running about 10 minutes late so it lost some custom to the 21A. I recently rode the service between Peterlee and Seaham and it was packed there was one person standing too. Also recently rode it between Middlesbrough and Stockton and had a good few on.
To me, the X7 seems a much more attractive option - nicer buses, better value fares, more connections etc. But lets see how it goes, I think the X21 will be withdrawn after a year.
I really hope the X21 can be a success too, as I like having a direct bus to Sunderland and not have to change buses in Durham or Peterlee and I will certainly be using this service on a regular basis and hopefully it won't be withdrawn after a year or so.