I fitted front and real lockers to my NAS D90 and it transformed what I could do with it (admittedly, some pretty difficult stuff, bot not "real" US-style rock crawling: just tought obstacles on overland trails in Colorado, Arizona, Utah, etc). And, although I may not do as much tough stuff as before in the IG, I want the lockers for the ability to pull me out of these situations. I have used both rear (regularly) and front (not nearly as often, but in specific situations where the front had the traction the rear did not).
Another reason for optioning the lockers is that they are a bargain, and the thought of waiting for an aftermarket solution, that might not come, could cost a lot more and not be as elegant an install, pushes this to the "no-brainer" side.
And finally, if I sell, the factory lockers will be a strong selling point.
This is similar to optioning the winch. I have used my winch on many,many occasions, both for self-recovery and to pull others out of situations. And, although it is expensive, the possibility that an aftermarket solution will work out cheaper is, to me, doubtful. Aftermarket will entail a complete new front bumper, wiring and the winch. And I saw some people quoting ~$1000 for a winch: for that, you get Walmart quality. Fitting less than a top-of-the line winch seems a ridiculous idea! And a Warn Zeon will cost well over $2k...... Factor in the new bumper, wiring and labor and you easily reach or pass $4k.... for something not as elegant as the factory solution....
And again: an aftermarket winch/bumper solution will kill much of the resale value.... (Looking at the market for NAS defenders, if I had left mine in a garage since I bought it (new in '95) I could ask $100k. But for my ultra-capable off-road example (with everything including lockers, upgraded suspension/drivetrain/brakes/tires, built in engine-driver air compressor, engel fridge, etc, etc.... and the trail bumps to match.... I will have to find a specific buyer and might get $30k.....
The Grenadier is an expensive vehicle, anf financing it with all the (practical) options seems to me the best way to go, for ultimate utility and (eventually) resale.