Same here. I have one, not the EX, but the standard, that I've been using for a year. It has the velcro straps, and I've been able to attach it to my front rack (which is not Topeak), but it's not as steady. I noticed on REI not too long ago that it now says that it cannot be used with non-Topeak racks. Maybe that does mean that they've removed the alternate attachments. But really, for touring, I don't know if that's what you want. There's plenty of other, more generic, bags out there. I love my Topeak bag, but that's only because it locks into my rack so easily. You take that away, and it's just another bag. Also, for touring purposes, you probably want full panniers, depending on how heavy you're traveling. I find one drawback to the Topeak MTX is that the fold out panniers don't seem like they'd have as much room as other panniers (although I haven't done a real comparison of specs), and if you leave them folded up, the trunk is fatter than necessary and can interfere with installing full panniers. I just got a slimmer trunk bag (Ascent) because I can't use the Topeak with my grocery bag panniers.
I love the Topeak rack/bag combo, but I do think either part loses a lot without the other. Things don't sit as solidly on the rack because of the bag track that's built in, and bags don't sit as solidly on other racks for the same reason. But put them together and it's easy on, easy off, very solid. However I've read on here that folks who use the Topeak rack fully loaded find it less than steady.
Now if you were going to use the fold out panniers, they loop on to the bottom of the rack, so, provided you have the velcro straps to fasten it to the rack at the top, you may find it perfectly stable.
But in the absence of a Topeak rack, I'd solicit advice on what trunks other folks prefer.