Hi, there. I only have the Alexa, and it is a beautiful bag. The leather is super soft and smooshy, and the smell is divine. The PS1 looks gorgeous in photos, but I haven't seen one in person yet.
The Alexa is a fairly light bag, and I have stuffed it full (I have the regular size in Ink...there is also an oversized version) without any weight issues. I have treated the bag to protect it from water, but I haven't been caught in the rain with it yet. I have heard of the lighter colors (oak) having some color transfer with blue jeans. But if you treat the bag before wearing, the color should come off with a baby wipe.
The buckles are a nice matte light gold color, but of course they are faux buckles. There are snap closures on the back sides of the buckles. It's a bit annoying to get in and out of if you are in a hurry, but I find that is true of any flap bag with any sort of turnlock or other secure closure.
Also, keep in mind that if you are on the shorter side (under 5'5 or 5'4) you may have to have extra holes punched into the strap. Mulberry seems to have designed the bag for someone tall.
Pfers own every and size and color available so far...so if you have any questions about a particular size or color, someone in the Mulberry subforum should have an answer for you! There are tons of photos and modelling pics over there as well.
Good luck deciding!