AusBonsai

Just bought a packet of these. are these okay to use on trees in training?

Yep, no problem

I haven't used this product myself, but personally I would be surprised - no shocked, if it wasn't great stuff. I have yet to find a Miracle grow product that doesn't work.

Slow release products are usually very good. It is best to mix them in the soil as opposed to laying them on top of the soil as they have a tendency to release all their fertiliser on very hot days, say above 35 degrees. This can lead to overdosing on fertiliser asunder fertilising as no further fertiliser is being released and you think that there is plenty for the next 3-6 months. This happens with all brands so be aware.
Also the amount of fertiliser released is not enough for gross feeders like figs, eucalyptus etc. so a supplementary feed using liquid fertiliser every week or two is required for these types of trees.