How long does the charge last on them? Would it be wise to order two sets?

I ordered just 5 (in case 1 was bad), charged em up and got 7.1V shown on my DX4R.
Used it on 3 different RC's, total of about 1-1 1/2 hrs and its reading 6.4V. Got my alarm set for 5.0V so I think I may have a ways to go. Great batteries especially for the price.

Can anyone recommend a low cost case that'll work for the DX4R?

I use a lunch box cooler for mine, the soft ones. I also have two sets of the nizn batteries. My radio started acting up and I lost brakes and reverse. I am going to have to zero all my settings and start over.

I think I found the problem I was having, I zeroed the brake amount on the main page, and this was causing the reverse issue. For some reason I can bind a Blue rx easier than the Spektrum ones, go figure. It shouldn't be that way though. Plus the bind light is easier to see as well. Way to go Spektrum, really!

I have noticed that mine also doesn't like to go in reverse. Sometimes I have to turn the steering or go forward a hair to get it to go into reverse.

I haven't updated the firmware yet, could this be solved with a newer firmware?

Yes.

My problems with reverse went away after I added 100% brake on the main page. The car you see in my avatar is my first painted body.

anybody knows the latency time in comparison to the KO EX-1/Futuba 4PKR & the Sanwa M12?

Not enough that anyone could notice! We are talking milliseconds.

if you read up reviews on the M12 a lot of people turn up the latency time because the response is almost immediate.

I have gone back to the SR2000 rx's for now. I believe the higher voltage from the NIZN batteries has solved the problems I was having.

What were the issues?

Just a quick question, what is the purpose of a 4 channel radio for surface vehicles? Gyros and telemetry or something?

A lot of recreational Rc vehicles use a separate servo for reverse gears,drift box,gyros,cooling fans etc...