The special trainer cost 46T to get the 25 y/o player from 114% to 120%, as you can check from the pic. Which happens to be exactly the price as buying 50 greens. If I hadn't bought the trainer, I would've definitely bought greens to since I had tokens to spare and no need to buy more players this season.
6% AvQ upgrade requires 90 single skill upgrades (the player was low 114, I think there was about 86-88 left). So the player would have to gain about 1,8 skills for every green pack spent, which wouldn't be achievable with a 25 y/o player.
My intention was to get the player to seven stars soon anyway and since it took less resources now, I can spend greens more on my younger, quicker training players. The fact that the trainer boosted grey skills more is the only thing that makes me think whether this was a poor investment.