Hi again Simon,
I am going to shock you now, my Shurflo backpack is very similar to your pack, however it has three speed settings and also and audio beep for low water level and for battery running low.
Now here is the shock, this retail much the same £260 + Vat and postage. I imported mine from the states, I paid £70 for the backpack £70 postage and £40 import tax total amount £180.00 and it is the latest Shurflo model.
I do have the same complaint though - I have a client who has a side window on her house and the only way to get to it is via a side field. So I had to strap the backpack on and walk half mile up this field, I wasn’t happy lol, needless to say I emptied it out to do the return journey. Good idea about the trolley, I will look into that now.
Andrew