I've been using my Lightsaver Miser tailcap for approx 1 year now, and thought I would make a brief report.
In that time, I have used two different setups with it: LF HO-E2R with two IMR 16340 and LF EO-E1R with one 16650. The most usage has come from the EO-E1R and 16650. In a years usage, I have not had a single failure with the Miser tailcap. However, there are a few things I have noted.
1. My EO-E1R lamp seems like it has darkened quite rapidly. I have been using Lumens Factory lamps for many years, have owned many different types, and have a pretty good understanding of the rate at which they darken. And I feel that this lamp has darkened faster than any other I have owned/used. A large amount of the usage the lamp has seen has been from the lowest output mode the Miser allows. At this point, the bulb is VERY underdriven. We know that a lamp, when underdriven TOO much, will allow black deposits to develop. I'm thinking that running the lamp on the low mode might contributed to this lamp darkening very quickly. However, being a tiny sample of just one light, I cannot say for sure. Hopefully, others can comment of their experience.
2. Although I have not directly measured it, apparently there must be a high amount of resistance in this tailcap. During a runtime test, a new, freshly charged Keeppower 16650 only ran for approx 75 minutes using the EO-E1R lamp. Far less than one would expect. There is also a small, but noticeable decrease in whiteness/brightness when switching back between the Miser and factory tailcap.
Overall, the Lightsaver Miser tailcap is one of my favorite pieces of kit I've ever owned. The biggest mystery to me is how this amazing little tailcap has been so criminally overlooked is beyond my understanding. How these things actually work, and how/why they are priced so cheaply is also a mystery. I would really love to see someone with the know-how to tear one of these apart and give us some specifics of how exactly they work.