They are a great Jack but you do need to know how to use them and be confident with them. You can even use them as a winch to get out of bogs.
I would recommend a good brand. I have used a Hi Lift branded jack for nearly twenty years and it still operates like new. It is impotant to keep them well lubricated otherwise the pins wont snap across, this then is when things can get dangerous, as well as sinking, over balancing etc etc
Yes the standard 4' jack fits in the RFSV bar attachments.
Regards
Scott