I have both the TFS-S3/8 and the TFS. Both are great but I prefer the TFS-S3/8 for two main reasons. The first is that the TFS has plastic feet that go over the spikes. This seemed fine at first but I soon realised this is an issue. The plastic is very slippery on hard surfaces such as concrete or any uncarpeted floor. The rubber feet of the TFS-S3/8 are much better. The other reason I prefer the TFS-S3/8 is the size. There is nothing wrong with the larger TFS spikes but I prefer the smaller of the two. Overall excellent product.
Side note. I added some Sugru to the bottom of the plastic feet on the TFS spikes and that has been working great.