I have both the Taylor(FAS-DPD) and the Spin Touch and I've tested on my neighbors pool (mine still being built) and the numbers from both the Taylor and the Spin Touch nearly almost always match. I would be extremely interested Pool-Medic on the source of the inaccuracy results you speak of.. Not trying to pick a fight - I am legitimately interested in this as again my numbers match very closely.
I'm not sure where the inaccuracy come from, but they are there. I frequented a pool store that used the Spintouch and several times I took them water to test after I tested with my Taylor K-2006. A couple of times they were close, but several they were way off the mark.
The first problem they had was the Spintouch has a limit of 15ppm FC. When I took over my pool from the previous homeowner (a puck and shock guy) the CYA was in the range of 250. To follow the [FC/CYA][/FC/CYA] ratios my minimum FC was 19 and I usually targeted 23 or so to stay above the minimum. They couldn't test that high..
Secondly, the CYA limit of the Spintouch is 150. With the Taylor drop based reagents I could do a diluted test and at least get in the ballpark and see how my CYA reduction program was working.
Even within range, there were times that the Spintouch results just were not right. Why? Who knows, but I can only surmise that there was only one or two employees who followed the Spintouch cleaning protocol. When the machine was clean and dry it probably gave fairly good results. If not, again who knows.
The consumer version of the Spintouch is the ColorQ-7. We have multiple people show up here each year happy that they found a "geek" product to help maintain their pool. Almost all abandoned its use due to inaccuracies and inconsistencies. We even had one member test the same sample of water three times in a row and ended up with three different sets of results. Here is an example of a ColorQ post:
ColorQ vs TF100 and here is a review where the Color Q was used alongside a TF-100.
Test Kit Comparison
Keep it clean and dry any you may have good results. But, TFP will never recommend a Spintouch or ColorQ mainly due to the cost vs. the know accuracy and simplicity of drop based testing.