Howdy Darkspark, and welcome to CPF,
The NovaTac series are very nice lights. I think one of the nicest features of the programmable model is that you can setup the UI (user interface) to work the way YOU want it to.
You see, some folks like their light to come on in the lowest mode first, and some folks like their light to come on in the highest mode, while others would prefer something in the middle. With the 120P model you can choose to have your light come on at ANY level you want....... and you can even have it remember the last mode you were in and come on at that level if you want.
That, combined with the fact that you can set it up so that no matter what level you are currently using, you can have access to the highest level by simply pushing in on the button.... and when you release the button it goes back to your currently selected level. OR, you could program it so that when you press the button it goes directly into tactical strobe.
So, you see, it's the variety of options and possible ways to configure the light to YOUR style of use that is what makes the 120P so intriguing to many of here..... combined of course with it's ability to use RCR123 3.7 volt rechargeable cells and it's rugged and nicely finished case.
Personally, I think the only flicker that is acceptable might be a small momentary flicker when you change between levels, which I've only seen once or twice with my light....... anything else is not something you should expect, even on the lowest levels... which I use regularly on my light.
However, and I've said this many times, I think that when you buy a light with this kind of advanced electronic control that it does open the possibility of having more problems associated with those electronics, but that is a tradeoff I'm willing to accept for the kind of flexibility and control I get in return. Plus I know firsthand that NovaTac customer service is very responsive and that this light has an excellent lifetime warranty against defects.
As far as whether to get the T (tactical) or P (programmable) model, well..... you can program the P model to work exactly like the T model, and you can buy a tactical tail switch as an optional accessory at Lighthound.com...... so for me, I see no reason to buy the tactical model because I like the option of changing the light if I want, and you lose that option with the T model. But, some folks just don't want to fool with the programming, and I understand that, in which case the T model might be the best choice.
Hope that helps. Have fun.