Well, it seems as though there are enough of the new MT-4s and related TX gear out for comparisons.
So let's have 'em, I want to be convinced that the new MT-4s is so much better than my MT-4, for me to go for the upgrade. Just to tell you, I love my MT-4.

Well i look at it this way. I have a Sanwa/Airtronics M11 that I've had for quite a while. The new M12 looks awesome but I'd only use 1/4 of it's functions. I hardly use a lot of the functions in my M11. To upgrade to the latest radio or version of the one you have would be pointless if you don't use all of it's functions, plus if your current radio is still performing well without any issues, I'd just keep it.

It basically comes down to this:

1. Do you need a backlit screen?
2. Do you have the Sanwa esc and would like to make esc changes from the controller?

If you said 'Yes' to either, the MT-4s would be worth considering. If 'No', spend your money elsewhere

The 4s and ESC combo is so cool. Had a ton of fun my first run out making adjustments to the ESC from the drivers stand. If you love the MT4 then the S is your next radio. Same frame with pretty much an M12 inside, I love it!

Thanks guys, I think I'll wait, I still haven't explored all the potential of the 4, and I don't drive in the dark.
That ability to adjust ESC from the radio is pretty though, I'm not that familiar with Airtronics ESCs but, I'm sure they are as good as the rest of their product line.
I've always been a Castle guy, but that's another thread.

Does the ESC have blinky mode and if it does can you put it in and take out of blinky mode remotely? This of course would open a can of worms for blinky classes.

im just waiting for a hardcore review of the esc vs the orion r10 for smoothness and punch. and blinker mode and adjustments. if someone can positively say dropping the orion for the vortex zero is due to similarity in performance and not needing the additional program box, id be totally stoked. nevertheless, i will prolly upgrade soon to the mt4s from an mt4 and just get the speedo too.

I wanted the wm4s so bad...

Yes it has blinky mode, but it has to be power cycled to take it in and out of blinky. This prevents the situation you are eluding to.

To me its quite simple.

If you believe that low latency is the thing for you, you go for the fastest radio you can afford.

If you are on at "budget", you choose MT-4S, if not, you go for the M12.

If you are a low latency believer (like me) and know that the MT-4S is nearly four times faster than the MT-4, there are no question.

If you do not care for the lowest latency, and don't mind the lack of backlit display, AND if you already have the MT-4, why bother then, you already have a good radio.

If you DO NOT already have a radio, I can see no reason for not paying a little extra and get the MT-4S which right now is the best price/performance radio available.

As for functions, I don't buy high end radios for functions, I buy them for low (stable) latency and adjustability features.

I drive 1/8 e buggy. I need very few functions that even a 50 dollar radio features.