I had a plate made similar to the vikan head, fit's into the pole and connects to my trolley, the spray nozzle was the hardest thing to sort. ended up cutting the nozzle of a metal watering can and it was araldited to the head. It lasted until the end of the job, but I kept catching it on the roof spars and it be came loose.
I've got to send it back in for the guys to have a play with it. Cost me a £100. I believe that a napsack spray will be better than the trolley as the pump creates to much pressure. Once the head is sorted, need to refine the trigger, but I won't need it until spring, so going to look at it again over the winter months.
They reckon they could make them a little cheaper if enough interest, but as I haven't refined it yet, haven't bothered posting it.