I have the MFJ-762 version. I swept it with a VNA and it was extremely close to spec. It is limited to 125 mW input. I purchased it used for $10 or $20 a few years back. At that price I thought it was cooked, but all is good.
I use fully variable 0-20dB attenuators for satellite equipment and only to adjust for highest possible signal without getting desensed or get overload issues when using antenna amplifiers. Those where less than $10 when I bought them.
I think the type in the picture are for lab use when you have to have exact calibrated values to work with.