Bought tickets online for Atletico Madrid-Celta Vigo game and im very pleased with the service. As i travelled to Madrid few days before the game, i ordered e-tickets which they send 24H before the game. You get a download link and then you have to print them.
Tickets arrived on time, no problems, good seats.
Getting tickets just before the game can be somewhat nervous but overall its a good place to buy them. Reccomend.