I am testing a 5-25x50 Vudu with MD3 reticle. Unfortunately, I do not have the 3.6-18x44 Mark 5 here, so I am going off of my recolleciton, but I am comparing the Vudu to some of the same scopes I used with Mark 5. At the same magnification, their optical performance should be broadly comparable. The Mark 5 I had here had less CA and flare was a little better controlled (common issue with short scopes), but if you are not using a clip-on, keeping a sunshade on the Vudu really helps with flare.
Honestly, I would have preferred the Vudu in a 4-20x configuration, than 5-25x, but it seems to work well as is (and my primary interest is using it on gas guns where 4x is nice to have). There is definitely a weird aesthetic appeal to a scope this short, but honestly, if you are not looking for compactness, you can probably get better optical performance for the money.
However, if you are looking for something short, this is easily one of the better options out there.
I tested it on a very accurate 16" barreled 5.56 AR-15 and it was an absolutely perfect fit there. The gun balanced reasonably well with the Vudu and the scope is easy to get behind. I hit everything I aimed at and while there is obvious CA when the conditions are right for it, overall image quality is quite good. I did not go above 20x very much when shooting, but that is pretty normal for me. One important factor was that the parallax did not shift POA in any significant way.
Basically, you kinda have to decide whether that short overall length is really important to you. The Vudu seems to run right around $2k, and for that money there are several larger scopes that will perform better optically, but you pay for that with packaging.
ILya