That Triac is overpriced. For that price, I'd want a newer one with a BT30 spindle, 8 position tool changer, built in coolant, and lots of tooling included, along with details of how it's been retrofitted to run Mach.
Similarly spec'ed non-modified Triacs normally go for under £2000 on eBay auctions, and a no-detail retrofit adds no value to the machine. It may even de-value it, depending on what's been altered.
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Provided the seller is selling it with the Coventry Quick Change chuck still installed, new holders are in the region of £80 each, so tooling cost can quickly add up. It is a pretty good quick change system though.
One thing to be wary of, is Triacs came with 3 different spindle tapers. Earlier ATC models came with a BT35 spindle, later ATC BT30, and then non-ATC ones might of came with either of those, or even an R8 spindle. BT35 tooling is pretty hard to get a hold of, as it's now a rarely used size.
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Routers are not limited to 2D. A well built one will handle 3D work just as well, if not better than a mill, it's just they usually run far higher speed spindles, which means you have to run smaller cutters. For aluminium, routers can often be a better option if you're doing a lot of finer details where smaller cutter sizes are needed.
For example some basic figures from a speed&feeds calculator, gives a 6mm HSS endmill a recommended spindle speed of over 11'000RPM in 6000 series aluminium. A 6mm carbide endmill is over 20'000RPM.
Obviously those spindle speeds are dependant on the machine being able to move fast enough to maintain a meaningful depth of cut.