I have a couple of thoughts on this. What follows is only my opinion.
First, a microscope is in the “nice to have” category for almost all purposes. A good headband magnifier is way cheaper and is in the “must have” category, and we don’t have a decent one. We could by 6 really nice headband magnifiers for the price of one lower end (price and usefulness) stereomicroscope.
Second, for some categories (like pliers, cutters, tweezers), expensive gear gives a hobbyist (or even professional) only marginal benefit over cheap gear. For other items (soldering iron, microscope) the difference between the entry level and the good stuff is game changing.
I am in favor of finding something usable from the science lab for now, and holding out for the Mantis for an eventual purchase.
The Mantis scopes have a much more forgiving eyepiece, good depth perception, and the stand (bolt down or clamp down) allows convenient positioning over a wide working area. Overall more flexible in use, with less neck strain and eye strain. If I could only have one objective, it would be a 4x, but a 6x would be fine as well. 2x is not much more than a head maginfier, and at 8x, vibration and shallow depth of field start to be an issue.
The disadvantage of the Mantis is that you have to wait a while to find a good used one on Ebay for under $1000, but they do show up with some regularity. Working heads without the boom go for less–I’ve seen them in the $500-$700 range, and the booms have gone for $150-300. Again, this requires waiting and judgement. Ebay is a lot less risky for these purchases now than in the past, as it’s policies have shifted toward buyer protection.
The original Mantis and Mantis Elite are great to use, and the Compact seems similar.
Here is a summary of the differences between original and elite, from EEVblog:
Both the original Mantis and the Mantis Elite can mount two objectives.
They both can be fitted with 2x, 4x, 6x, 10x, and 6x SuperLong-Working-Distance objectives, but the Elite also fits 15x and 20x objectives. The new objectives have different product codes (but I’m not sure if they are compatible).
Only the Elite has LED illuminators (it has one for the left and one for the right). The Elite can also use an epi-illuminator (a halogen bulb that shines down along the same optical path as the image). The original Mantis only has a diffuse halogen light. The original Mantis bench stand version (Mantis FX) also uses a halogen substage illuminator for transparent samples, whereas the Mantis Elite substage uses LED lighting. The Elite is available with an articulated boom, in addition to the standard boom type like the one on the original.