Not commenting on the Stepmores machines as I have no experience of them but one thing I do have is experience of other chinese made machines. To me the problem comes from the very fact they have to compete on price with other Chinese manufactures. The net result is that they are built to price and the build quality suffers badly for this and the Stepmore machine IMO won't be any differant.!

They are mass produced so the attention to detail and quality control in areas that matter is just not there. The result being you have to sort it out your self.
This is ok with electronics as they can be replaced but when it comes to structure of the machine that's quite a differant story. Often they are so poorly made or weak that it's just easier to start again.!
Now often these machines are ok for cutting woods etc and get away with it because of the low accurecy and tolerences required but when it comes to aluminium they really struggle and show there poor quality.
Yes they do a stronger Cast machine but again these things will be made to the lowest possible price and when it comes to Cast iron the quality of the cast makes all the difference and IMO the Cast products I see coming out of china range from scrap to just about acceptable.!!. . . Now if you get a bad cast then your in world of even more pain as it's not easy to repair or true up.!

So what I'm saying is I wouldn't go rushing into buying any chinese machine until you can get a Solid report from someone using the machine for exactly the use you intend.
I can tell you from cutting huge amounts of aluminium that any machine mostly doing this needs to be very well made and I'm not just taking about strength. When it comes to harder materials like Ali then it very quickly shows any weak areas of a machine so build quality and attention to detail are just as important as the design strength and it's here IME that the chinese machines fail badly every time.

Regards multisided cutting then it's not just a simple case of remove and flip over if you need accurecy. For accurate turning you will need solid and accurate fixture jigs to help ensure accurate coordinates are re-established. It can be done but needs careful thought and planning.

Regards the electronics then that smoothie thing I wouldn't touch with a barge pole for creditable routing/milling machine. Ok for 3D printer etc but for routing/milling then it's just not upto the job and will give poor performance in comparison to good digital drives and PC with motion control card.
Also I don't see any way you can view the cutting path/G-code or control things like feed or spindle speed overide etc which is essential when milling.
Often you need to tweak the cutting conditions on the fly while working and this lack of interaction is unthinkable to anyone who's used to cutting materials like aluminium etc. This Ok with 3d printers or pick-place machines where you just hit start and walk away but milling then no way would I want this inflexabilty.!

Next about spindles is the 1.5Kw is just about enough for cutting aluminium but I'd recommend you go with the larger 2.2Kw for spare over head plus the larger ER20 collet system allows larger range of tooling.