They are 100% reliable, very precise and result in excellent calibration results. I originally designed this system for a Max Metal delta printer but it worked so well that I used it on my Rostock MAX V3 and I'm going to retrofit my other deltas with it over the coming year. There are 2 significant aspects to this new mount.
1. The FSRs are now positioned outside the build plate perimeter as you can see in the renderings below. This minimizes the "teeter totter" effect when probing 1/2 way between FSRs. Moving the probing points out significantly decreases this effect.
2. The second improvement comes in the way the FSRs are mounted and how they are triggered. In my previous mounting system, a printed plunger moved inside a printed cylinder. This led to one of the two reasons folks had problems with FSRs (the other was that their bed is not stiff enough - this mostly applies to the Kossel Krowd™ that simply used glass with a Kaptan heater). The plunger system works reliably but only if you use high quality prints and prepare and lubricate them properly as I've described on multiple forums and here. Otherwise, they can bind ever so slightly, leading to inconsistent triggering. The good news is, this issue is easy to identify and correct. The better news is, this new system eliminates the problem altogether! Here's what it looks like:
With this new system I simply adhere the FSRs and rubber plungers with sticky tape so they are constrained in X-Y but free to move in Z. The FSR has a sticky back, just peal off the protective film and stick it to the top surface of the printer. The plungers that come with the Ultibots FSR kit also have a sticky back, so peal that and stick it to the top of the FSR sensor itself. Now you put a small dab of silicone seal on the top of the 3 rubber plungers (a SMALL dab) and press the FSR Plate onto them and allow to cure.
I actually don't bother with the silicone, I just have my plate resting on top of the plungers. I've never had an issue with the plate moving. I am working on a simple printable locator that will attach to the top printer plate that will keep the bed from shifting but since this has been working so well, I have not bothered.
Finally, you can see in rendering below a recent modification - the FSR Plate now has three ears. In my V3 photo at the start of this post I'm using big binding clips. I needed to add 3 additional rubber plungers under the FSRs to make room for those. But, by tweaking the FSR Plate with the ears I can remove those and use the ears to attach the Onyx/glass with the little blue (or other) holddowns. I do one other thing on my printer, I adhere the Onyx to the top of the FSR Plate with a disk of the 3M 468MP tape we use to attach PEI. This holds the Onyx perfectly flat while allowing it to expand and contract in the X-Y plane without buckling. It works quite well.