The spiral cutters are good for solid woods, they can come in both down cut good for deep work shaping or up cut (watch jigs and depending on depth you may need clamps), they can also come in roughing and finishing form also. I like to go for thicker shafts as possible on my cutters for heat dispersion and stopping the fracturing.

As for jigs I make for nesting etc I use Birch ply and more often than not 25mm thick. MDF lets vacumn straight through and you loose some suction-try a sheet of paper on mdf to see it in action, to prevent it you must coat your mdf with glue/paint etc. The ply does not need any coatings and the jigs last longer, ply has cross banding grains between the layers, the edges do not leak either accordingly.

As for cutters I purchase replacement tip types as these keep up the quality in moulding and work performence, they work out cheaper in my industrial setting anyway but are of course more expensive to purchase new, I usually buy two bits where I used to buy three of each size in single/double flutes to keep up production and always have one on the machine. Tips cuts this out as they are always available and the second bit is if I have a mishap and I need production to remain uneffected.

I stopped grinding my own cutters and heads some years back. I find now that repalcement tips on my heads is more efficient and gives me better quality of mould. I replaced my Weinig Unimat with a powermat with CNC auto heads/tool/mould auto recognition and quick change facility, the tips was the way to go for me as the Powermat needs a grinder to do profiles greater expense, replacement tips like I have now was the way to go for me. The quality and setup times have given me greater efficiency between quick changes.