I’m not really sure as I’ve never used the EV trainer myself, but I can recommend a much cheaper alternative:
Friend safaris are free and easy to use (all mons are lvl 12-18) and this guide also detail how many EVs you get from each mon in their safari.
Or you could search by the preferred EV in this guide and use the Pokemon Locations guide on the wiki to find the locations of those mons. I would recommend the first option though, as the levels of the mons that give 3 EVs tends to be higher (40-80 range),
Hope this helps!