Thanks all! With regards to new vs old, all my tools so far were bought new as I like having a warranty etc. But also with secondhand, its the lottery you mention, both from a function perspective but also whether or not stolen etc.
Where I am sat with the Festool domino is knowing that this is a luxury item in my situation, its for my own house renovation i.e. I'm not on the clock. So to pay full whack I've just got to get my head around how beneficial it will be to the cabinetry I've got planned. That said, if I drop a grand on something I can sell for 500 quid after a couple of years, I won't lose too much sleep over it.
re doors, I do similar but use redwood frame and MRMDF inserts. Thus far I've been using a Wealdon combination bit for the rails and styles as wanted a more decorative look for wardrobes but for the downstairs cabinetry will opt for something closer to shaker in style. I can't quite picture how you are using the domino to assist with the doors, assuming used to increase the strength of where the rails meet the styles?