I've used both of these (picnic tap and ball lock flow control nukatap). I think they're best at different things. And depending on what you are looking for in particular, you'll find one more suitable and the other unacceptable.
Picnic Tap 2.0
It's compact so it fits easily in your keezer/fridge on your keg. That's good, because it likes to stay cold (otherwise foams like others have noted). Mine has been drip-free and leak-free, but obviously that's not everyone's experience. So if you have a non-leaky one, you could leave it sitting on your keg in in your keezer to take samples as your beer carbonates and/or matures.
There are two big downsides for my particular usage. 1) Its tiny size is also a downfall. With it sitting on a keg, in a keezer full of other kegs, I couldn't get a cup under it to pour my sample without a lot of hassle. I also tried it in what I consider "picnic mode" where I have a keg in an insulated bag with an ice pack. It was too short to stick out of the bag, making it non-functional as a picnic tap. The other downside for me was the pouring speed. Painfully slow for me. If I were just filling a couple ounces in a glass for a taste or to check carbonation, this obviously wouldn't be an issue. But to try to fill a pint of beer to drink took way longer than my patience cold tolerate.
So if it were called Sample Tap 2.0, and that's how you planned to use it- inside a keezer/beer fridge just to collect small samples, then it's a perfect solution.
Nukatap Flow Control Keg Faucet
I was impressed with how this worked. Having tried the non-flow-control taps attached to a ball lock, I can attest those are a foamy mess directly attached to a keg. (But to a growler with a really skinny dip tube they do work, though.) It's size is smaller than a length of tubing and the standard cobra/picnic taps with all their various troubles, yet big enough to stick out of my insulated keg bag. It is not drip free, it's like any keg faucet. There's always a couple drips to fall after you pull your glass away. So it's not a good solution to sit on your keg in your keezer full time.
It does allow you to fill a full pint glass in a normal amount of time, but you do get a bit more foam. But not huge amounts. See picture below, for beer from my cold keezer (16 ounce glasses). Nukatap flow control adjusted to fill glass in same speed as my keezer (12 seconds):
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