Are these two rc transmitters any good?

In my opinion, I would say no. I would stick with the Traxxas Link 2.4ghz system since you are putting it in your Slash anyways. You can get one on ebay for around $40 and it really is a very good system. I use one Traxxas controller for all 6 of my RC's. If you get the Link receiver (which is included in the cost of $40) 2218, it has 5 channels, so if you are hooking up accessories it will handle it. Then if you get another RC, or already have another one, all you need is the 2218 receiver and you can use the same remote/transmitter. Just my opinion and what has worked well for me.