I am buying an iMac 21.5-inch with VESA bracket instead of the Apple stand. Which brand of mounting arm is recommended for adjustment of reach and height? I am not able to drill walls and a heavy stand is not easily portable -- so I need a G-clamp to desk or (preferably) screw-into-desk for security. Do bracket manufacturers supply the iMac adapter screws or must I buy these separately? I can't believe how little help Apple is in averting use of their very-limited-adjustment stand! Thank you.