I think k and MXE can be compared alongside, they are very similar in effects but each one once it's reached those certain points takes different parts and enhances them. I don't always find k really wonky, a lot have the headspace trip more so.
K is more shit talking than introspective in comparison to MXE but I feel that MXE after daily use has a poor introspective side as it seems to be a reviewing of oneself but on a sober mind is complete bullshit. Both affect perspectives pretty similarly, although I think k has a more instant perspective change (feeling small/tall) while MXE perspective changed is obtained by sitting and staring.
The main difference I feel is that MXE didn't have much stimulant properties, but more so opiate, there was a warm blanket feeling throughout, which although seems to feel comforting ended up just causing fiending. K if in the right setting always gives me a great buzz afterwards, or in low doses, I would much rather mix k and MDMA than MXE and MDMA. Although in exchange, MXE seems to offer some nice empathy on the comeup, but I feel as the peak hits it declines massively.
The holes are slightly similar too, although I found I could get out of the M-hole, whereas k your thrown in and stuck for the ride. MXE seemed to be disturbed a lot more easily, but the rooms/scenes were much smoother. I actually think MXE might be better to hole on for the first time if your interested in trying the k-hole but unsure if your ready.
I prefer k, I can take it at higher doses and fall into an intense hole. While MXE at higher doses just leads to a state of complete confusion and temporary blindness. But I found tolerance with k was harder to maintain, but MXE still grew rapidly too.