I was about to order my 14.5" M4 upper from Bushmaster for my RR sendra conversion.  I'm building this up in pieces -- so far I have a Knights RAS and a QD bracket only.

In terms of ordering the upper, the next thing I'll add with likely be an Aimpoint.  If I'm doing that, do I need a flip down front sight?  BM will install one of their front sights for me at no extra cost other than than $100 bucks they charge for the sight.  Is that worth doing?  Or should I order the standard front sight?

BUIS are a good idea. I am planning to get one from Bushmaster myself.

Which rear sight are you going with?

I haven't decided yet.  As I'm going in stages, I thought I might start with the sight on the A3 handle.  People seem most fond of the GG&G sight, I'd like to hear what you think of that.

GG&G products are nice, but in short supply it seems.
I went with the PRI front, very basic, and has a hood feature that protects the front sight post. If you need to attatch a sling GG&G is the way to go.
Also check out the ARMS #40 rear sight.

What kind of front sight block do you have mounted?

Why did you place the rear sight that far ahead?

Uum, have you practiced the indians coming over the wall.  Cause i would suspect that the rear sight would be unusable if the elcan was and AFAIK the elcan's going to take some time to get off.

BMAS triple mount gas block - does that work if you have a Knight's RAS installed?

Phil and all
I did quite A bit of research on this subject
I found the following, take it for what its worth.
-BMAS Flip upsites Lock in place up and down and are realativly inexpensive compaired to others.
-GGG are excellant except the one for the picatinny ral does not LOCK up, therefor if bumped it flips down, Surprise!
-Best Back up site IMHO is the ARMS#40 or #38 swan sleeve w/ #40 attached.
-I dont really see a need for a flip up front site almost all optics can see over post if mounted with proper mounts.
I personally run an ARMS #38 Extended rail which includes the #40 site with a fixed front site on my Armalite. M15A4
this allows me to use an Aimpoint without the spacer, low profile, and cowitness if I choose or not. When I mount my TA11D on top instead of Aimpoint, I can only barely see the front post in bottom of the scope, If I look for it.
If you need the front flip up, get one that locks!!  BMAS front site is very rugged but get the Tri-rail gas block and site that fits it, dont get the V-match type and clamp on site. it is a bitch to keep from rotating during clamp  on installation, youll drive yourself bonkers.
chuck