I have an older version of this rack. Used it for one trip and some commuting. It worked pretty good. I could not prevent side to side sway, but a friend who has the new version and is using their spacers doesn’t have any issues.

I used this with the topeak slide on case/panniers and like them a lot. It did need a spacer, which my lbs had. If that 20 lb max were higher I would have given 5 stars rather than 4. But that said, I think that the weight is really limited by how strong your seatpost and seat tube are.

If you have a large-diameter seatpost this is probably great. I tried it on a 27.2 (using the spacer) and it wouldn’t stay put no matter how hard I cranked it down. 2*.

I purchased this with the rack that keeps panniers out of the wheel. The weight limit seems low enough that one couldn’t really stuff both panniers and the rest of the associated rack without hitting this ceiling,and when it’s loaded down, the thought of bouncing it on an off-road ride is just asking for a failure. To be fair, I have bounced a lot of weight on this on a few rides with no failures. The side-to-side sway was mostly a problem if I leaned the bike a lot (bad form when standing and pedaling, or taking a fast corner). The sliding/locking mechanism is super nice for day trips though, where it’s convenient to remove the bag from the bike.

This rack is fantastic! Not a bad price with an REI October discount. Just used it the first time on a bike packing trip this weekend with a buddy of mine. Works great for those rocky trails, perfect for a dry-bag or sleeping pad, tarp, etc. Doesn’t get inb your way when riding on a trail or even pumping up a big hill. All around great light weight rack. Great buy.

AZ Explorer I couldn’t agree more…This rack saved me when the seat bag route didn’t work out for me. I did exactly what you said with a dry/compression bag. Check it out:
http://www.bikepacking.net/individual_setups/tucsonprerunners-3-day-setup/

I’ve got exactly one shake down afternoon run and one two day(one night) bikepacking trip on the latest version of the MTX(V-type, specifically). The shakedown run was loaded and on some very twisty, fast singletrack; almost certainly more demanding of a ride than my two day trip which ran me through mostly refuge, fire, and levee trails. I do use the rubber spacers and the rack held tight. It carried a sleeping bag, tent, snacks, and a water bottle; probably around 10lbs. I’ll probably toss the tent up front next time for weighting the bike more evenly, the majority of my carried weight was on the rear rack, with a little more(change of clothes and another bottle) in a frame bag. I had other goodies packed in my hydration pack. The handlebars were empty, so I’ll balance things out a bit more next time.

I hate to be a downer but eventually this style of rack is going to break. I know of at least 6-8 of them that have broken for Tour Divide and GDR racers. My advice would be to save your money and get a Revelate or Porcelain Rocket, etc. seat bag.