DrD,
I'm not sure that either of the guides would help you with chairs. I can't think of any task, at least. Those types of mortises typically need special positions for each mortise.
They can help you for doing the cabinetry, but it also depends on how much of that type of work you do. For example, for your Arts & Crafts doors, you can use either model of guide and blindly machine all of the mortises without having to layout each door separately and mark them with pencil lines. So for example, if you have all of your stiles and rails cut and stacked in a pile, you can machine all of the parts without having to pre-match which stiles belong to which rails, etc. But if you're only making a couple doors at a time, then you lay out all 4 pieces for each door, mark which stiles and rails get joined, and machine them up separately. In that case, the parts for each door have to stay separate from other doors and can't be mixed and matched.
For the same reason, they are also handy for machining drawer boxes. You don't have to pre-identify which pieces belong to any specific drawer box. Additionally, where the MGS guide is best, is when you need an offset between sides and the front/rear pieces (like when the sides are taller than the front/rear). This is where the multiple positions are needed, so you can offset one location 1/4" away from another location.
The guides do have other uses, but these are the only ones that you mentioned. So I can't speculate on other tasks you may have.