Looks interesting. I'm not a CNC guy, so don't have any great insight into it.
Do you have an idea of what you want to make with it? If you're going to be making stuff that requires a 3-axis CNC, then it is probably good, but there are other options, although they have different constraints. E.g. you could get a smaller 5-axis CNC (https://www.pentamachine.com/all-products/p/pocket-nc-v2-10) for a similar price. But, it will depend highly on what you want to make with it and whether it has the capacity to make what you want. Here's that one in action: https://www.youtube.com/watch?v=nBBG-8j15Yc
I had not seen that one, though I wanted more flexibility to make larger parts than its work envelop allows. Interesting option none the less if I have a need for smaller 5 axis parts. I try to design my parts so it only requires 3 axis, but it's true that isn't always possible.
Also I do know they are looking at making a 4th axis upgrade to the MR-1, though I'm not sure how much z-axis travel that will leave (z-axis travel does seem to be one of the bigger limitations on it so far).
For added Z height, you could probably make some spacer blocks to lift the whole X/Y gantry above the table, similar to a mill column spacer. That could give you increased Z clearance, but wouldn't increase Z travel (so you could end up being unable to reach all the way to the table). But there would be ways to compensate for that, like installing a sacrificial pallet.
Ideally, you would use some solid steel bars that are match ground parallel, but even steel bars that are fly cut on a mill, or the CNC itself, should be adequate. You'd probably need to fly-cut the table flat if you were using just milled parts. Getting a couple of steel bars ground parallel shouldn't be too expensive though, if there's a shop near you that does surface grinding. I presume you could probably run a small fly cutter in it. Size would be limited as the shank is 1/2", but you should be able to use a ~2" diameter fly cutter with a low depth of cut.
That would be a fairly big project though to get set up properly and something you wouldn't want to be swapping in and out all the time. Having just trammed the column of my mill, it's a bit of a pain. Every bolt that you tighten moves things.
If you did get the 3-axis, you could probably increase its accuracy by getting some parts of it surface ground. Looking at the photos, the construction looks to be mostly formed plates that are welded together. I would imagine that the relevant surfaces are machined after they are welded together, but they are unlikely to be ground. So, if you were having trouble with or trying to get more precision out of it, you could have the surfaces that the linear bearings mount on ground flat and parallel. But, you're talking probably a difference in a few tenths over the length of travel.
Yea, that is the trick. It wouldn't be fun to have to keep raising and lowering it, being that it doesn't change the z travel. I suppose if I had a major project that required it, I could do it if I had to. I saw where a couple people have done some custom mods to it and raised it up but mentioned it may impact rigidity. I think they were just doing all aluminum or other soft metals though so it wasn't a big issue for them.
I know that during normal assembly they do have you mill the work plate parallel to the XY axis. There is also this modular work holding system for it (saundersmachineworks.com). It might make sense keep it raised up a bit to compensate for the added height of the work surface if this was used. Hopefully it wouldn't affect rigidity too much.
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