In use the j-pole is lightweight and works well. I also noticed that it has some directional properties, the body appears to sheild (absorb?) the RF slightly. Due to the length of the 'pole, it can also drag bits of branch and birds nests down on top of you, and on one occasion a dicarded ice cream wrapper (wet side out - nice), anyway, mind you dont hang yourself with it! One other warning, motorists tend to watch the pole rather than the road if you are near civilisation, swerving, hooting and wrong side of the road motoring are all symptoms. You have been warned!
I have used this from 2100 feet asl, with 20 watts from the FT857 with QSO's from the Pennines into Wales, south Coast and Scotland. It also works on 70cm too. For best performance suspend from a 6m pole and feed with a few meters of RG58.
On the rucksack from around 800 feet fed with 5w from an FT60E, distances of 150 miles are not uncommon.