Where you place the pick up is very important. You actually want to read it at a location that has variations as that will give you the quickest indication of low pressure ... but you have to 'learn' to use it (when to look at it, how often and under what conditions).
I know that the OEM oil pressure guage on my TLC is worthless. It doesn't read low pressure even when I'm very low on oil.
Actually, let me caviate the above statement: it's worthless as an absolute measurement, but ... I've learned that when my oil level gets low, the pressure reading varies more with engine rev.