I think it really comes down to your setup and what you do day to day.
If you run with lights, fore grips/vertical grips, lasers etc. and don't usually need a magnified optic adding the Elcan can add some extra heft to your set up that is already loaded up. This upsets the balance of your M4 and it will not handle as nice as it did with just a red dot. Depending on what type of shooter you are it may not matter but if you are doing courses or something where you are handling your DD all day it may start to wear on you and you really start to notice that you have to put more effort into what you are doing.
If you run a red dot and magnifier set up you have to make sure you have no issues with your eye's (i.e. astigmatism) since the red dot will look like a fire ball, the Elcan has fantastic glass and you won't have this same problem with it. You will be able to pull the magnifier off when ever you want if you don't need it or flip it to the side which is handy.
I have had a few Elcans, red dots, magnifiers etc. and I feel even though the Elcan is a beautiful piece of kit and I have one on my MK18, depending on what carbine/rifle I've tried it on it really upsets the balance and puts a much larger footprint that will bang into more stuff, get caught on more stuff etc. Because of this I only install it on certain setups.
The Elcan is also a much larger investment than a good red dot/magnifier combo but again the quality is second to none with the Elcan, but if you really don't need it or don't want to spend the money then the red dot/mag combo will work just fine and give you some flexibility.
My best advice is to ask your local firearms supplier, friend or someone at your range to have a look at their set up or if able try it on your M4. This will tell you right away how it feels and if it is for you. Each of these set ups aren't for everyone as you can see the shear number of 1-4 Elcans and red dot optics/magnifiers for sale on the EE so it is best to window shop before buying.
Just because it works for someone else doesn't mean it will work for you. Don't take peoples word for what's best, try and find out for your self what's best for you and your setup.