Was about to get a toy- then I did some research...

[Juranovich]

This is the problem people only focus on those who have had issues, probably because they shout the loudest, but for everyone that as an issue there are 100's more who haven't and work perfectly fine.

Typical case of selection bias... This is what they warned us about in uni!

Not quite sure what your meaning by Less hassle.?

You said that profile rails are better and less hassle, but I think I got the drift now.

The square rails for me are may be the most important part of the machine in the long run, so there should not be any doubts about that. In fact better buy a smaller size square rails than round rails. mean 15 instead of 20 size , if machine is not intended for heavy duty use . You can always use one carriage more as they are cheap. rail is heavy hence expensive to ship. You get what i say?

[...]

I buy from these guys https://es.aliexpress.com/store/822038 12 and 15 size. Have not bought from them 20 size , but their rails are very good quality and price. Custom size also, contact them. make sure to buy the long carriages.

I hear and thanks for the link (and thanks to everyone who's provided useful links to vendors). Theoretical modelling is one thing, but sourcing good materials is always extra hard when you lack experience. Much appreciated!