Just stick to Trainline
I was excited when I found Trainpal - the prices looked good and it was good to have an alternative to Trainline. However, everything about it is worse. Firstly, they used to not support in app tickets which meant that after a long flight, all my friends at LGW could get straight onto the platform but I had to wait in line to print my tickets. Now I see they do have tickets in app, but the payments fail randomly. It's just a far inferior experience.