Can't speak to the WM-8H, but have run either the WM-8M (or it's older/cheaper sibling - can't recall exactly) and for the items I was chipping the tractor wasn't an issue. The in-feed was; both the roller and the belt system driving the roller - at least it was on the old rusty unit I'd borrowed.
Was chipping a mix of semi-dried out Bradford pear trees (dropped the entire tree that was 40' across), pin oak trimmings and some other small trees/bushes. May just have been the specific unit, or the weather and wood amount/conditions, but the belt slipping for the in-feed roller and the in-feed roller wanting grind rather than pull material in ended up making burning the wood easier than chipping it. When the
chipper fed things in it did great, when it didn't ..... Again, I'm not going to judge the entire product line on my experience with that one unit I had borrowed (and would caution others against doing so as well), but it was a data point that helped educate me on a few things to look at when it comes to buying a wood
chipper.
Having said that I'm still looking to buy a Wood Maxx
chipper in the next few years, but am more inclined to go with the
WoodMaxx MX-9900 even if I need to reduce the in-feed rate. From what I've seen (both from that unit I'd borrowed and commercial trailer mounted ones I've used) the energy in the fly-wheel is more important than the input HP. Higher HP can result in faster recovery times and potentially reduce the RPM drop, but the flywheel is ultimately there for a reason..... so I'm inclined to go with the
chipper that has the biggest heaviest flywheel my tractor could handle.
Likewise the larger in-feed greatly helps reduce the amount of cutting that has to be done for highly forked limbs/branches to feed into the the chipping blades. Which is usually more helpful than being able to feed the larger solid pieces (given trees tend to have many more limbs than trunks :thumbsup

. ...and if the in-feed is built so that it can grab and really pull (and maybe even snap smaller branches) into the
chipper then :thumbsup::thumbsup:
(btw have bogged down a large 12" 89HP Vermeer tow-behind with semi-dried 6-ish inch plus crape myrtle trunks/trees before so I know more HP isn't always the answer ...however, a good/strong grabbing in-feed system and being able to control the in-feed rate are very much useful things in a wood
chipper)
Just my :2cents:
One last thought when chipping branches/trees; a
cordless reciprocating saw with a wood or pruning blade (depending on how green the wood is) is an extremely handy thing to have on hand -- perhaps even more so than a gas chainsaw.