When it's being looked through, the NECG peep is no different than any other peep.
No peep sight will work great in extremely low light as well as a low-powered scope, and I've tried many sizes including "no aperture insert" for a ghost ring effect.
The best you can do on a peep would be to either go with the aperture insert removed - a "no can do" on the NECG sight, since it's used to lock the elevation adjustment - or drill out the aperture (from the front) with the largest drill bit it will take.
While most of the available fiber-optic beads work very well in bright and overcast daylight, if you used too large a F-O bead, it will work against you in dim light (like in dark swamps, and at dawn/dusk) - where a smaller/finer F-O bead will serve you better.
You do give up some low light capability using a peep vs a scope, but not as much as you might think. I would say less than 5 minutes of legal light time. It depends on the aperture size, front sight size and type, the distance between the two, and your eyesight. In any event the peep will be superior to the factory open sight. Take your rifle out in the low light conditions you expect to use the rifle and if you can see the bead you'll probably be ok with the peep. Having said all that I have not been handicapped using a NECG peep on a Mk II RSI with the factory bead. I would try the factory bead first and would be careful about using any glowing type bead as it will affect your aim more than a plain gold or white bead as lighting condition change. Glowing front sights tend to "swim" depending on lighting conditions. I use the large aperture and for me it works well. If you have not used a peep sight before, you will be surprised how accurate you can shoot. It definitely "opened my eyes". With a target I can see (I use a six inch spot at 100 yds) my groups are no different than using a scope. I believe using a peep has improved my shooting overall and it's a lot of fun. My RSI just looks wrong to me with a scope on it now and the whole rifle handles better. I have a Weaver K4 set in rings and zeroed but I prefer using the peep. In the rain/drizzle the peep is probably superior to a scope. I think on a #1 in 45-70 a NECG peep would be a perfect set up and look much better than the best scope, especially if you have to use offset rings to make it work. The NECG sight is relatively cheap as aperture sights go. The only drawback is that the aperture locks the elevation setting as pete44ru said. If my #3 in 45-70 had a rib it would be wearing one now vice the 1.5-4X scope that's on it. I say go for it.
The NECG peep for the Rugers is a well made, if rather "chunky" in design sight. It works well and is very sturdy in hard use. One of its design features requires the use of a screw-in aperture to lock th elevation slide in place so it really doesn't work as a ghost ring type of aperture sight. Further, one is limited in how large an aperture insert can be used since the sight will cause flattening of the circle as viewed through aperture due to the channel in the sight forward of the aperture.
None of this is intended to discourage potential buyers of the product. It is simply information one might appreciate when spending close to $100 for such a product. I like both NECG apertures I have, both the one for Ruger and a sight made for 22s. I do think the basic design of them could be improved some however.
[If my #3 in 45-70 had a rib it would be wearing one now vice the 1.5-4X scope that's on it.]
NECG now makes several more variations of their peep, one for rimfire grooves, another for European scope bases, and a fourth for Weaver-type bases.
If you don't already have Weaver bases on your #3, it's nothing to switch over to a set.
Understand Pete. I just don't know if I want it stuck out there on that base. With the Ruger mount I have been able to switch back and forth between the peep and scope with no loss of zero and just haven't decided if I want to try it on that weaver base.
Not that I know of. I like the XS rear sight because it does not obscure the view of your target so much. However it requires drilling and tapping of your receiver. I made my own detachable using an XS rear and a Burris, Ruger to Weaver adapter, for my RSI. It came out pretty slick. I will post a pic when I get my RSI back together.
I had one on my 6.5x55. It worked fine, but I didn't like the attachment either because 1) it didn't feel like it was ever going to tighten, no matter how much the screws were turned (like the metal was soft, and continuing to yield the whole time it was tightened) and 2) I came really, really close to running out of windage adjustment for it.
Shooting with it was fine. But I was unimpressed enough that I ended up selling the sight.
I do think there is a significant loss of shooting time with a peep...it may not be a huge number of minutes on either side of sunrise & sunset, but in my not-too-limited experience using peep sights on lever guns, the minutes you're losing are prime shooting time (at least where I live).
Todd, you adjust it the way you adjust any XS ghost ring sight. Loosen either the right or left windage screw, several turns and screw the aperature up or down the desired amount and re=tighten the windage screw. I used an XS low Weaver Back-up sight, one of the adapter bases of a Burris Ruger to Weaver adapter base set for Ruger M77 and a 4-40 flathead screw. And a lot of careful cutting, filing and drilling/tapping one hole. When I attached the sight to the base, I used epoxy as well as the screw to make it a permanent strong bond.