Dark choccy = phsyco
Sorry just re-read my post and maybe a bit direct. Too much dark choccy this arvo. Makes me a touch phsycotic.
We get a lot of posts on here where people ask whether this is better than that and so on, and people will always put an opinion that is ultimately their own.
It's all down to your preferences and budget. If you want a marker that needs little attention other than a few very basic ups and just a lube every now and again, go for the PMR, if you want a marker to tinker with and add to over time, get the Ion.
Although being a proud ion owner, would find it hard to recomend an Ion over a DM4. Best thing to do is try and have a go of both PMR and Ion and see if you like. However maybe a newer model DM is the way forward?