[rcheshire (Rowland)]

The advantage of the AT is weight, the electronic package and reliability. I have agonized over buying one for several years.

EDIT: so as not to be misleading and referring to the potential of these devices in general, favouring the design over similarly priced conventional drives, including the capacity to produce very low PE values - the need for correcting the drive because of inherent geometrical characteristics is noted...

The tangent arm design is attractive because of the effective diameter of the RA gear and the very fine resolution of the worm itself. Even without a microprocessor the AT would track accurately.

EDIT: given the capacity to fabricate this kind of performance with relative ease...

I think the <5 arc seconds peak to peak (no correction) is conservative. A good tangent arm is quite capable of that.

The reason I didn't buy it, was concerns about rigidity - I think these are unwarranted providing the tripod / pier /wedge is solid enough.

A second reason was the quality of the finder scope. Which I hope is fixed, after mentioning its shortcomings (build quality) to the manufacturer. I bought one to align the Tracker - and it worked very well with some modification.

If you have a solid tripod that can be accurately leveled and stay in alignment when locking down, the rest is academic.

I think about the AT frequently, like something I should have done. Occasionally, some of the big US stores sell demo packages at a reduced price.