Wouldnt this be fine and dandy to CC some heads.

no and yes
No if you do not have a known standard to calibrate it to;and yes if you do.
I see the tip as a bit of a problem.
But it also kindof depends on the accuracy required. If you're just curious as where ABOUT your c/r is, then fine. But if you are building to a specification, or are running c/r on the edge of detonation, or trying to match chamber sizes,then not so much.
If you buy two of them, you can calibrate the tip of one by drawing fluid from the second.You might get accuracy to .3cc to maybe .2cc, who knows. In a streeter, .2cc error in one measurement may not be a big deal, but if you start adding .3cc in the head plus .2cc in the bore, well then, it's starting to add up.If you're building a 9/1 engine it's no big deal, but if you want to be sure that you can burn 87 in your 9.8er, well you might want to rethink that, cuz .5cc at that point could be .5 /10 of a point of compression in a 360, and almost .7/10 of a point in a 318. Not much, but perhaps enough to push you into the next grade of fuel.
Truth be told; up to a 1/2 a cc in a streeter is probably not going to cause problems.
I used something like that,which I bought at the local vet-shop,for one of my engines.I did it a little differently tho. I did all the measuring and math as usual. Then after the engine was assembled, I rolled it over to put some plug holes at the high points, and injected oil into the chambers to measure the total chamber volume. I had a good match.It was a streeter.It burns 87E10 on 10.64 Scr(al. heads),which was about 78.0cc. If I was .3cc out, the final c/r calculation could vary between 10.58 and 10.70

You should also know that using water and your thumb in one of those is very tricky. The rubber seal loves to stick to the plastic sidewall, making small changes very difficult. I combated this with Silicon O-ring lube.I got some hi-grade stuff from a Fuller Transmission rebuilders outfit.Good stuff.The rubber seal tolerates the silicon, but almost anything else will swell it, and then it is useless.