I actually tested my Slik Pro 330EZ with a Rolleiflex 6008 Integral and Schneider 150mm lens, with a laser light on top of the finder. I fired with and without mirror lockup - the difference was astounding. Without, the light would very visibly and forcibly shake, with mirror-lock up and remote release I could not see any movement whatsoever, no matter how much I tried. Real-life pictures reflect this.
I had considered the tripod too flimsy beforehand (it was not purchased for this specific rig), but still liked it, as it is light-weight and easy to throw over my shoulder (in a tripod bag), so I take it along rather than leaving it at home.
That said, I've also grown used to a Sirui monopod - with mirror lock-up and remote release, it is able to deliver astounding results.