I purchased a number of these strobes, both to put on life jackets (water activation) and to serve as navigational beacons while boating at night (manual activation). I have always found that the water activation works well, and the flash is very easy to see from a 180 degree field of view (note that if the strobe is angled away from you it is much harder to see), but over time I started to encounter other issues with these strobes. About 15% of mine at some point have had small amounts of water infiltrate the transparent dome with the LED, even without any real submersion. This never seemed to affect their functioning and I was able to remove the water by drying them in rice, but it gives me pause about using them as critical lifesaving gear. I was hoping to use some of these strobes with NiMH rechargeable AAs, which work well in ACR strobes, but these UST strobes don't seem like the slightly lower voltage and stop flashing after a disappointing amount of time. I think I got maybe 24 hours on rechargeable batteries before the strobes stopped flashing and went to a very dim, steady-on light (better than nothing I suppose). So I recommend sticking to alkaline or lithium primary batteries. These strobes have a metal wire that encircles the batteries, and on that wire is a metal spring. I found that this spring over time damaged the plastic outer wrapper of some of my rechargeable batteries, especially the higher capacity ones that are ever so slightly wider than normal AAs. If you need to change batteries out in the field, be careful you don't drop the wire because it falls out very easily, an annoying design flaw. Most critically, I had one strobe short out, become very hot, and suffer complete physical and electrical failure after I turned it off. As you can see in the picture, the metal wire piece was completely blackened, the batteries were obviously toast, and the bottom of the plastic body broke completely (I guess from the plastic getting hot and maybe pressure from the batteries inside?). I burned my fingers pretty badly when I tried to dislodge the batteries, which had gotten stuck because of the aforementioned metal spring and thermal expansion. The reason for all this seemed to be in the head of the strobe unit--repeated manual activations and battery changes over time caused the metal wire piece to wear through some plastic on the interior of the head, exposing it to a wire lead that thus shorted the batteries. Because I used these as navigational markers, I recognize that I probably manually activated these strobes and changed their batteries much more than a typical user (both actions wore down the plastic head), but it seems like a problem that could've been avoided entirely with better design choices. So all told, I rate these 3 stars. If you stick to lithium batteries and test the strobes occasionally, they should work just fine as locator beacons on PFDs. But for safety equipment I would like to be more confident in the waterproofness and reliability of the unit. Small design improvements would improve the usability of the strobe and would have prevented the total failure and subsequent burns I experienced with one of my strobes. If you don't need the water activation and want to use rechargeable batteries, I recommend the ACR brand strobes.
