Apart from calming down with the rudder inputs I haven't had any issues with glider powered converstions.
Although one of the sods when i pulled the power on him for a PFL started gaining altitude. When asked "what are you doing" his cunning plan was to move the aircraft 10 miles or so along the ridge gain another 500 ft then land at a disused field. Reckon he would have done it as well.
They are though utterly pants on the radio.
And it isn't hard its all about currency. Most spam drivers don't practise steep turns PFL's and the like. They maybe do an hour a month bimble or burger run and thats it. Maybe every 2 years with an instructor they hamfisted get through an hour and promise themsleves they will go up for an hour to practise but they never do. If the pilot has been a reasonably high houred instructor the currency doesn't seem to matter so much. Its proberly to do with the fact you have demonstrated the things that often your muscle memory is well and truely programmed. And demonstrating a PFL from the RHS but doing a LHS "circuit" means that 90% of the time you don't see the field your going for anyway until you turn in for your constant aspect approach. Tends to develop your SA about what where how your doing it.