Yeah, sek is right. These are really intended for tabletop rotational use where you can do a rotation around an object and even keep an object perfectly centered in the frame without any panning of the head. The wheels can be locked down in any position, so you can do it in a straight alignment as well and I have a link to my vimeo video in the other thread, I think which shows the dolly going straight as well as around a glass. People have also made platforms that fit onto light stands which hold the dolly up in the air so you get more of a person-height dolly move.
You're right about the time and complexity though. it would be much simpler to make these without any moving parts.
You're right about the time and complexity though. it would be much simpler to make these without any moving parts.