There's a thread on the zone where someone bought a cheap one and took it apart. The assembly was rough and ready and maybe slightly out of square.

My main reason to buy rather than build , is time.
I've been nursing my 'allthread' Z axis on the CNC for months, but it is in use all day every day. I have the new parts... ballscrew, rails etc. but not had the time to do it.
Same as I bought a WC spindle and VFD 6 months ago, and not even had a chance to power it up to make sure it works !

As for the tubes having a lifespan ... I spend more than the cost of a tube on router cutters ... so not an issue really

I'll put photo's and a mini review up when the laser arrives :)