Hi. I have just received the Mars universal stem and spent a couple of hours trying it out, and here's the initial thoughts.
What you get.
Full stem.
All the gromits for all the models it is designed for on a single rubber wheel, just twist off the ones for your make of coil/machine.
Fixing plate for the control boxes that require it.
Instructions for the fixing plate.
Arm cup strap
Machines for this stem
The uni stem accommodates a lot of machines but check carefully before you buy it. If your machine has battery pods housed in the stock stem, or cables inside your stem, then this isn't likely to be an alternative for you. It appears to be designed for models with a mounted control box and an outside wrap around cable to the coil. In other words, machines that can take all detecting parts away from the stock stem. As I stated, check first that it's right for your machine. Contact Mars if your not sure.
Assembly
For me personally, assembly was a doddle, 5 minutes without instructions, but I was fixing the Sorex Pro to the stem and I don't require the fixing plate. Sorex and Berkut slide straight on. For other models there are some small screws with a fixing plate, and obviously this will need more time and care than it does for the AKA machines. The instructions warn you that the modification to the underside of other control boxes is irreversible. Find some feedback if you want more info on this specific aspect.
Build quality.
Very well put together. Solid. This is a tough telescopic stem. My initial thoughts are that this is a solid build and it is not flimsy in any way. You really feel as though you are swinging a quality product. Mars have clearly thought about durability. If you have broken your stem and need to replace it, (and if this stem is designed for your MD), then in my opinion I doubt this would disappoint. The arm strap I received is only just big enough, I have small forearms, it needs to be longer.
Looks and design
Sleek, smart, with good ergonomics. I love the feel of the grip, a chunky pistol style hand piece that is a joy to hold. Overall it feels and looks very nice. Being telescopic, it may lose the black colour on the lower stem as it rubs over time, but from new, this thing looks and feels pretty darn cool.
Weight
As you would expect, it's not heavy, however, neither is my Sorex. Sorex is pretty light. The main reason I bought it is due to a problem I have with my weak arms and joint problems. On longer hunts the sorex causes a slight ache in the forearm. The MARS stem won't solve this for me. In fact it feels very slightly heavier than Sorex stem. There is more weight in the MARS at the grip end due to the chunky and solid pistol design. I needed to extend the MARS longer than the Sorex stem to counter this, which helped a bit by giving better balance between grip area and coil.
Two things you must remember here, Sorex is pretty light, and I cannot tolerate much on my arms. For many machines the MARS stem will be lighter, and for many of you, you won't have the problems that I have due to my manky arms. So if your buying it to reduce weight, do more research than I did ! This was completely down to a bad assumption on my part, it's not a criticism of the stem. Most of you will probably consider it acceptably light, but you should compare weights to what you already have if greater lightness is your goal. In many cases it will probably help, but not for me.
(I apologise that I cannot state the weight)
Practical advantages
Being able to slide this stem down into a compact size will be something many will love. You will need to consider how you fix the cable, perhaps a permanent tape close to the coil and more flexible options further up so you can reduce it down easily for transport and carrying from the parking spot etc. You could argue that the same can be achieved with most tubular frames, but there is no doubt in my mind that the quick release snap locks make it easier, it's designed to be a slide down easy carry stem after all.
Final verdict
Very well built, a stylish stem that will appeal to many. If you don't use Sorex/Berkut then please research the modifications and consider if that's what you want to do with your control box. It doesn't appear to be a huge undertaking but I can't advise on something I haven't had to do. I understand that there has been good feedback from people who have bought one, and I can understand why. When you hold it, it feels solid and serious. In my opinion the hand grip is brilliant. And it looks superb too.
Hope that's helpful.