I have a Topeak beam rack (with the side rails installed) and a couple of different QR trunk bags that I use when commuting on my FG. As long as I really tighten it down (and don't overload it - I normally only carry lunch and maybe some extra layers), I find it plenty stable. Not sure how well it'd work if I had to carry a laptop, full change of clothes, shoes, etc. On my winter commuter, I installed a regular rack (and fenders) because I can - it's better.