Well, i have a dilema here - need a new hunting searchlight( not a gunmount one) , it will be probably moded, so pls help me decide:
- which one has better flexibility, durability, mode options and overall quality
Wondering several days allready 
Well, as you probably already know, the TK75 can expand its battery capacity, I run 1x extender on my 3xLED TK75. I just bought a TM16, but it’s not here yet. The TM16 has a much lower lowest mode than the 2015 TK75.
From what I know the TK75 is heavier, the Nitecore is built to be lightweight. With the crazy discounts I’ve seen, the Nitecore is a good bit cheaper.
I have a TK75 with 2 extenders. The light uses little battery holders that appear to do 2S 2P for 18650s. Looking at "hunting" is a bit ambiguous. Variables are terrain, vegetative cover, distance, length of hunt, prey. Way excessive for frogging or hunting night crawlers.
I have not done a whole lot of testing with the light. But it is certainly usable for an emergency light. Like seeing detail at a several hundred feet. Providing intense light looking through debris. With the 3 battery packs in the extensions (total), it gives long running time in comparison to similar output lights.
Unless you are hunting mountain goats (or UFOs), it should be useful. Hogs; no problem. Ground hogs - useless. It can also be a decent close range combat weapon.
Note that I am not a hobbyist. I just wanted a bright light to use on the property with good duration. We have forest fires and earthquakes.
Price-wise, the TM16 can be had for $116 with the discount code or during the sales period.
Doubt you can get the TK75 v2015 for below $150.
Weight wise, the TM16 is lighter and I do like the UI for Nitecore. So easy to get use to the 2-buttons, and the set-up is just nice. The mode sequence is just nice for me, from the low mode with 5 lumens output to the Turbo.
Flexibility, I think the TK75 has the edge over the TM16. You can use battery extender, the shoulder strap is also a nice touch as it can be tiring holding half a kg flashlight in your hand after a tracking for a while.
Quality wise, the TM16 is my first Nitecore and to be honest, I think the build quality is a notch lower than Fenix as I have few Fenixes, the first being the P3D Q5 that I have since 2008 that is still going strong. I hope the Nitecore will be as long lasting as the Fenix
After 2 days of thinking and reading i ended you with 2 orders 
After the evaluation i will just sell the other.