The 4x4 is a different pad from the pro. The Pro looks like it has external armor, where the 4x4 is sewn inside. They are making comparisons with the Race pads, which have a good rep. on the bike forums for staying in place, and fitting well. The Race Lite was a terrible pad, and this new pad seems like it is a replacement for that one. It does say that they are improved, and that could be the reason. It is still too new to have any reviews, but it sounds like 661 has been listening to feedback at least.
They don’t have pix on the site, but 661 still shows the 4x4’s in their lineup, and in stock. I don’t know how that translates to buying in Spain, but it may be something.
Here’s a link to the MTBR.com armor reviews. You may find something that’s easier to get in Spain, and fits the bill. I know it’s not uni specific, but I have been happy with my Raceface/Roach pads, and they aren’t either.
Unless you want to test out new stuff, it sounds like the easy decision will be the KH armor.
As long as they are big enough to go around your leg I would focus on the length. The Mediums were the ones that fit me based on the 661 sizing chart, but they were just a bit too short, and would ride down as I pedaled. The large would have been a little big around, but the length would have been much better. I ended up selling my medium 4x4’s and picked up a set of large Roach Indy’s, and they are a good fit.
When I’m wearing shorts the straps are loose (I can put like my whole arm between the strap and my leg), over jeans the straps are loose but there is no slack like when I’m wearing shorts. Occasionally when I wear soccer pads backwards to protect my calf, and over jeans, the straps are pretty tight.