The p10 is mounted all wrong for a mini diiger in my opinion, it would be a lot better on Big Bolts boxer, but on a mini digger you hitch it on half way up the mast so you have to lift it quite high (and consequently out at far reach) to enble enough height on strainers and other tall posts. I agree anything is better then a sledge but i think there are much better designs out there for minis. I would certainly look into the pecker cup ones, iv not used one of these on a small machine so im not sure how well they cope with large 7inch posts.
What i did was get a compact tractor model which had a 10ft mast and shortened the mast to 6ft, I then welded the digger mounting bracket down at the base of the mast so that when you lift it you can easily get the height for tall posts (i can even knock posts in on top of a bank). I then have two chains (one on either side of the mast) with about 4inches of slack- these are attached from the postcap to the base of the mast so that when you lift the knocker onto a post you can press down untill the postcap slides up the mast untill the chains go tight (about 4inches) and then start hammering, this gives you the benefit that the weight of the postdriver is taken by the post and you can also press down onto the post at the same time as hammering which makes it far more effective, the digger is also a lot more stable as the boom is not bouncing up and down each time the weight goes up. because the knocker is hitched to the digger at the same level as the post cap(at the bottom of the mast) you always get the full height of the mast for the weight to fall on every stroke.
The protech p10 weighs 190kg with a 100kg weight, this kind of weight at full reach is pretty hairy on a sub 2ton machine if there is any kind of slope. My machine weighs approx 140-150kg with a 90kg weight, you can fling it around no bother at full reach and because you have the ability to press down on the post it is actually more effective then the protech despite having a slightly smaller weight. I use mine in conjunction with a hydraulic auger which is neccesary to predrill prior to knocking in large posts.
The vector postdriver is the best commercially manufactured postknocker iv seen on a digger yet BUT at 220kg with a 100kghammer it is really too heavy to be used to maximum effect on a machine less then 2.5t.
Hope this helps- if the description of my machine made any sense.!