Interesting about the elastomers on the ST. They used to be three different colours, as for the LT. With the LT there is a pair of elastomers that are cylindrical so you can mix two to get five grades, (two intermediate) rather than just the three using them unmixed. We have an LT on our tandem, and an ST on the (adult) kids' tandem. My daughter was lighter than my wife at the time (not sure that's still true), and I wasn't sure we needed the LT in the first place, but the shop that built the tandem put on an LT. The 'pogo stick' effect would be more the case on non parallelogram-style shock absorbing seatposts. There are some in which the seatpost itself expands and compresses rather than keeping the saddle approximately a constant distance from the bottom bracket. This tends to get fewer favourable reviews from stokers.