I have the AEII for my Bronica ETRS and it gives me excellent results. The later AEIII overcomes some of the limits of use of the II. I find the metered prism to be faster than using a handheld, as it converts the camera to AE mode.
I find that I use my handheld meters about 75% of the time, easier to work with if wanting to be a bit more creative. I could easily live with the AEII full time due to results but to be creative requires adjusting the iso, etc., just easier to go handheld. Plus easier to go handheld if wanting to meter other than the area the in-camera meter covers which for me is very often.
Considering the average price of most metered prisms, a hendhald can be had for bargain pricing and can be used with other cameras. I use mine to meter my dslr as the dslr is just too much information overload when using its meter, detracting from the composing and developing the emption of the photo taking experience.
Neither of my meters cost over about $50 so it does not take big bucks to get an excellent meter; mine are are a Metrastar and Weston Ranger.