I think the TR1. is more reliable because the starter-gears is guided by a solenoid and not by spiral-cut gears. It's not smooth but it works! The most common problem (and not a big one) is that you have to clean the collector-area in the electric engine once a year because if you have a bad connection throug it the solenoid just clicks and nothing happens. Se my info-site; http://www.buf-online.kristianstad.se/~lars.sandstrom/starter.htm

I have Fitted a Suzuki GSXR1100 starter motor in place of the original, chosen because of its drive gear being identical,only longer. The later unit is fitted with four brushs and a roller bearing on the drive end. Finding GSXR1100 (L) starter motors should be very easy and cost effective (mine was $80.00 Australian second hand).A Ring will need to be manufactured to fit between starter housing and sungear/block housing, (I have exact dimensions if required).The end result is a powerfull,reliable starter that can be replaced easily if need be.

Well, I´ll try to translate the text;
A good drawing of how the startermechanism is workig. A common problem i that the solenoid has bad connection with "ground" through the collector an brushes, #8 in the picture. The symptom is that nothing happens when you press the starter button exept for that the oillevellamp is shining (eventually the solenoid is clicking). The remedy is to clean out all the coal-dust an rust from the inside of the starterengine. Take off the cover by removing 2 hexhead bolts and to long screws with cross-heads. Scrath out the spacings between the copperplates on the collector (about ½ mm deep minimum). Check that the brushes is not to short, otherwise replace them, and see that they can mowe freely in their holders. The springs tha presses on the brushes should bee in good condition too.
I do this routine once a year and the starter works 100% of the time!!
In other words; it´s a sound construction but needs cleening once a year. No need to replace the unit, save your bucks for something else!