I have used the nematodes in the link above but have bought them from gardening naturally website, a little cheaper.
I have used the nematode which kills vine weevils on a whole batch of field grown trees in grow bags and also some nursery stock that were all riddled with vine weevils. It was probably a little over kill as I had bare rooted everything and washed the roots already. Everything is doing fine.
I have also used the cutworm killing nematodes on my vegetable garden and the ant one when preparing the base for my greenhouse after disturbing a few ant nests when removing turf. All seem to have worked well.
They are a living product so have to be used within a week or two of purchase and you have to protect against cold temperatures as well for a while after application so can only be used at certain times of year.