Comment from someone who doesn't own a Niteflux product: I've read the comments from more than a handful of people who have bought the Niteflux products. Reviews tend to be mixed and from what I've read the customer service at times can be slow.
I like the concept ( wide rear lighting ) that Niteflux brings to their design BUT....I feel the design and build of their lamps is very simple and as such this should be reflected in the asking price, however this is not the case. In my opinion the Niteflux products are over priced. The Red Zone 8 was talked about for almost a year before it finally came to market. I don't know what the hold up was but it certainly had the previous buyers of Niteflux products quite flustered.
Yes, the RZ8 is definitely overkill but there are people that like the idea of overkill. Personally I don't think I'd go with the RZ8 but the RZ4 should be more than enough to get you seen anywhere.
On the other hand I'm very satisfied with the current offerings of rear self-contained mini-flashers sold by the many companies that make these kinds of lights. My personal favorites are two; Namely the Cygolite Hotshot and the Moon Shield. The Hotshot has perhaps the best UI in the market when it comes to rear lighting. It is very versatile. Some complain that the beam pattern is too narrow but with that said I've seen video that showed the Hotshot being more visible ( from the rear ) than the RZ4 at a distance.
The Moon Shield is my other favorite. The output from this lamp is wider than the Hotshot and more visible from the side. From a distance the two are fairly equal. The Moon Shield has three very useable steady modes, one strobe (flicker) mode and one flash mode. I like the flash mode. It is bright, it is highly visible both from a distance and close up. I do own a brighter rear lamp but truth be told, I feel just as safe with the Shield as with my other brighter lamp ( which has shorter run time ). I believe on flash the Shield is suppose to *run 7hrs although I've never confirmed that myself. The Moon Shield has a sister product made by Serfas although it is a tad over priced. Still it can be bought for about $50 USD which is not entirely unreasonable. The Moon version is available in the U.K., it has one extra mode. Best bang for the buck is still the Cygolite Hotshot.
( *Note: reported run times vary. It should be noted here that both the Hotshot and the Shield can be operated while charging. This should mean that if you desire longer run times that you should be able to use an external phone battery/charger designed to charge a USB device ( although I've never tried this myself I plan to ))