Dear Matthias,
You lose nothing, but gain a lot by using an F4. Even with MF lenses you can use all
metering modes including matrix metering. I have used a F4s for several years myself
now and most of my lenses are MF lenses. The F4 is really a superb camera in MF mode
since shutter speed and aperture are set the 'old fashioned' way. No fumbling with
buttons, jog dials, menu settings etc etc.
When set to AF you'll have a very sophisticated camera too.
About the build quality: I have shot about 950 rolls in the past
three years with this camera and it has NEVER failed me!
If you have any questions feel free to email me.
Best regards,
Bas Jordans