mm...I can't offer advice on which pro trolley comes out best, although I converted from trad to WFP about 7 years ago via a trolley system from Peter Fogwill.
But I do augment my van mount system with my own version of a WCW backpack that's been converted to a sack truck trolley system!

Not a lot of good to you if you are looking to go for a decent trolley system; however, if it is a case of adding a trolley system to an existing van mount system it is at least worth me outlining my method of doing so.
For me the backpack was for those occasions when lugging out 100m of hose either through a house or around terraced houses was unviable, the backpack gave me that viability.
But I very quickly realised that strapped onto cheap, lightweight sack truck [from Homebase] it really added to my versatility, my partner worked alongside me, and on residential work, one of us would take the converted backpack and go around the back, and the other would work the front...we worked very, very efficiently as a result...
A full pro trolley system = ££££ compared to £80 for the backpack and £25 for the sack truck...backpack battery soon got dumped and a small car battery replaced it.
Not forgetting a decent submersible transfer pump in the van tank of course to quickly fill the backpack....
Ian