Adding ghost ring sights to my 20 inch 8 shot Remington 870 Police and with all the options, I cna't decide on which is best. Strangely, the OEM Mossberg ghost rings seem like a very appealing option as I really like them and they appear to be a very sturdy design, no to mention affordible. I like the Wilson sights, but I have heard too many stories about them coming off during heavy use as they are "glued" on....for this reason, I have excluded them from consideration.
Do any of you used Mossberg ghost rings on your 870's? Who makes the "best" ghost ring sights and which are the most durable?

I'm in the process of adding trijicons to one of mine. I too am a little "skeptical" about gluing the front sight. I drilled mine for a 3/32" tension pin and cross drilled the front to the base. I also used JB weld for the "glue". (The adhesive was out of date with my sight set) It isn't going anywhere. Got the set from Brownells. Pretty cheap compared to the other options..

LPA/PSI.  Vang Comp uses 'em.  Very durable and relatively inexpensive.  Brownells has them, search for PSI shotgun

When adding ghost ring or rifle sights to an 870, you have to take into consideration the existing, original front sight.
In most cases, you have to remove the existing base in order to install a new base or sight.

Remington brazes the front bead or rifle sight bases on the barrel with a high-temp braze compound.
In order to remove the factory base, you either have to heat the barrel until the braze melts (this is a red heat), or you have to cut the base off.

Heating the barrel to a red heat "can" be harmful to the barrel, and since the heat destroys the finish and discolors the bore, you have to refinish the barrel and re-polish the bore.

Cutting the base off is a less damaging option which leaves only the base area bare of finish.
Cutting the base does take some good operator skills with saws, files, and light grinding to prevent damaging finish outside of the base area.

With the base off, you then are faced with brazing the new base or sight on.  Like removing the original base, this requires red heat to braze the new base and this again requires a refinish and re-polish of the bore.

There are two options that don't require heat.
One is a clamp-on front sight.  This works well:
www.brownells.com/aspx/ns/store/ProductDetail.aspx?p=9203&title=TACTICAL+SHOTGUN+SIGHTS
The only problem here is, there may be a compatibility issue with a front sight from one maker and a rear from another.  There may be problems with getting the gun sighted in if the sights are are too different in height.

The second option is the Wilson glue-on.  
While the IDEA of gluing a sight on doesn't sound good, it can be nearly as strong as a brazed sight if done properly, and is almost always stronger than an old-style screwed-on sight base.
The "secret" to a good mount job with the Wilson glue-on sight is first to get the sight and barrel CLEAN.  
I mean chemically, squeaky clean by using de-greasers until there is NO trace of any lubricant left on either.  This is where most jobs fail.  They don't spend the time and chemicals necessary to get all traces of lube off, AND get the parts DRY after.
One "trick" is to degrease the parts, then to use mild heat until lube in the pores of the metal and in the rough finish are brought out, then degrease some more.

A good "glue" are the higher grades of epoxy, PROPERLY metered and mixed.  Brownell's sell some of the best, although the "slow cure" more expensive types sold in hardware stores will do.
Here you want to get as exact a meter of the components as possible, then to mix for at least several minutes.  The better the meter and the better the mix, the stronger it is.
Try to keep as many air bubbles out of the mix as possible.

Coat the entire end of the barrel around the bond area with release agent to prevent the excess from adhering to the barrel.
Warm the barrel, (NOT hot, just warm).  Apply enough epoxy to insure there are no gaps or air bubbles, clamp the base down TIGHT, then put the barrel in a warm oven or under a heat lamp to keep the barrel at about 100 to 150 degrees for 4 or 5 hours or more.
This will insure a stronger bond.

After allowing a full 24 hours for the epoxy to reach full cure, drill a hole through the new and old base, and insert a solid pin or roll pin to lock them together.
Be SURE to keep the parts cool by using a drill lubricant, and by drilling in short passes.  Epoxy breaks down at around 300 degrees and a drill run too fast can heat the base enough to degrade the bond.

Mounted this way, the Wilson sight bond to the barrel is very nearly as strong as the original base under it.  
To knock it off will require enough force that the sight or barrel would be deformed from the blow.

I'll second the MMC ghost rings.  Properly installed they are tough to beat IMHO.  I had a set installed on a Beretta 1201FP and was very happy with them.  I think they would be great on the 870, and although they are a bit pricey you get what you pay for.  (My$.02)
Mike

I like the Mossberg GRs myself. I have them on my 870, and they are great.