I've used both products for years. Here are some of my thoughts on the topic...
I bought CataLook some years ago and spent a couple of years working with it. I found my store down constantly. The upgrade process is a pain. The documentation wasn't clear. They upgraded their own site months after I bought the product and lost me in their client db and stopped sending me updates unless I emailed them every couple of months and asked for it. I spent a good portion of my time trying to keep it running. From what I've read in forums, I think they've made some improvements in recent years. It was a painful experience.
So, I switched to ASPDNSF a couple of years ago (when it came out). Their DNN integration was problematic and I spent months trying to get it to run correctly. After a couple of releases, they stablized the code enough for my clients to complete transactions successfully. Their integration with DNN required users to enter their contact information 3 times in the user registration form and so I lost the majority of my business in that process in terms of shopping cart abandonment. I ended up with a stable copy of the DNN version but it didn't provide an intuitive user experience. As a result my cart abandonment rate was through the roof. I also wasted lots of time walking customers through the basic transaction profess. Their limited use of AJAX was disappointing. Their navigation approach never came close to meeting my needs. After lots of disappointments with subsequent releases (hoping for more than I ever got), I finally asked them to switch me from the DNN version to the ML version. I still haven't installed it yet because I want to provide my users with a seamless content and shopping experience.
The biggest difference I see between the 2 solutions is that CataLook supports integration between DNN portals well. ASPDNSF only allows you to put the solution on a single portal. That is a big issue for me as I have lots of portals that share users and content.
Neither solution met my hopes and expectations. I've worked in ecommerce for 15 years. It all comes down to intuitive, simple workflow and neither product does that well in my opinion. Both feel like they were written by programmers with little understanding of human behavior and how to predict, track and target behavior. If you use either of these products, your user-base needs to be highly motivated to purchase your products (enough to make it over the barriers they will likely encourage to get their needs met) and pretty techno-saavy. This doesn't describe the vast majority of online shoppers.
Hoping and wishing for a better solution...
John