there is also risk of injury and also time to get one star up ( like couple of days, instead of immediate gain )

but i agree, its better to do it this way. In 2-3 days you can get a SA on those fast trainers ( i have done it before ).

I have over 200 green packs but still i dont have the time and nerves to do this lol....or maybe i dont have a proper player to do it now, who knows..