The dP meter you found would be fine (no water doesn't get into it, if you mount it right), but it has two drawbacks:
1-it's battery operated.
2-It doesn't have an external output.
There are plenty of similar units on eBay that would do the same, and more, and are cheaper.
You want to watch out for the resolution, because a resolution of 0.1 PSI is going to be pretty useless. (this one can do 0.01 inches water, so it's fine).
The range is also important; this one is max 60 inches WC (~2 psi), which is good, but personally, I'd like it to be able to handle more, i.e. ~180 inches, or 5 psi, for those odd very restrictive blocks, at high flow rates (assuming your pump can handle it).
There's a critical piece of information missing about this product (no surprise there); the response time i.e. how long it takes for it to register a change (of X magnitude) in the pressure. I like to know what it is, because I'd like to quantify any oscillation (aka variations), on the 60Hz frequency, along with the resonent ones at 120 Hz and above, if possible. Entirely optional.
Otherwise, you can check the calibration yourself with a good old fashion manometer ("U" tube, always advisable; it should be part of your checklist before the start of each testing session).
I favor a model with an output, because I'm looking to log all of the data with a PC, but it's really up to you.
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