Got one and love it. I dont see any reason using the ratchet shifter is bad but the stock one could be just because you could accidentally go into reverse.
I agree with MeanMike, I don't belive it will hurt anything unless you are abusive.
I installed my TCI Street Fighter about 3 months ago and I really like it. It is a well made product and performs as advertised. Very easy install with common tools, it takes more time to remove the console and other interior panels than it does to actually install the shifter.
I shift my 4R70W manually quite a bit (probably more than I should). As long as you have a good tranny cooler and don't do it too hard/too often, you should be alright.
Car had a 4r70w, before switching to a glide month ago. The 4r had full manual valve-body...had to shift it manually. Had 2 trans cooler. Heat kills trannies. Had to watch that closely and let the trans oil circulate for a few after each run, before turning motor off.