The biggest problem with the round type rail and esp the cheap chinese type is the bearings quickly become loose and sloppy so lose accuracy and need regular adjustment.
They are no where near as accurate to start with compared to profiled linear rails which just work and last for years without any attention other than lubrication now and again.
They won't take the abuse Profiled linear rails will take and dusty or abrasive conditions will quickly take it's toll on them unless you take precautions to protect with wiper seals etc.

Like Eddy I agree these rails let down what looks like a nice substantial machine and IMO Profiled linear rails make the difference between Average DIY and Professional machine.
Don't look at it so much in terms of they are expensive which they are not in long run because they give a much better and far more reliable machine but more they will return there investment 2 fold later down the line if you ever decide to sell the machine as they will still work just the same and not be wornout plus appeal more to potential buyers who are prepared to pay more for professional looking machine fitted with correct components.