A brilliant idea, but flawed execution.
First, as other reviewers note, the circle cutter is problematic because the centre piece moves around too easily. Luckily there is a simple and low-cost workaround: simply fix the centre piece to your glass with a few strips of masking tape (I expect other tapes would work too, but I use masking tape as it leaves no residue). Simples.
The strip cutter is great - almost. I found it invaluable at first, and I have used it a lot for a year or two. I particularly appreciate its accurate steel ruler. But now I see its weakness: the plastic slider (the one that slides up and down the aluminium rail) has worn, and is now quite floppy. This means that cuts are no longer reliably parallel to the rail - they can be a few degrees out, or presumably they can be slightly wavy. This is especially noticeable with very narrow strips. Its annoying because this is unnecessary - if the slider were engineered better (OK, that means more cost, I know) it would not have worn. Shame.
The base is a sort of rubber. it is a nice, cutter-friendly, non-slip surface. But even after a year it STILL wants to roll itself up instead of laying completely flat so I have to use some home made weights (fused scrap glass actually!) to hold it neatly flat.
Let me know when the design solves these issues - and I'll buy another one!