Thanks for reaching out again. Yeah, simple.keywordinspector.com and keywordinspector.com are two different things (Although we are migrating everything into one). Moving forward simple.keywordinspector.com is what's going to be used solely. I'll ask James about why nothing is showing up. Make sure you are trying to get data from best sellers in your niche or top 10 in the keyword you are looking to rank for.
To answer your comment about how to use keyword inspector, it's basically reverse engineering and works best f you have a private label or exclusive bundle/product...
Say you have a private label cheese knife, you can go to the top selling cheese knifes and have keyword inspector do a search and see what the top sellers are ranking for. It will give you all of the keywords that people are using to find that item.
The gold is to see if those other listers are using sponsored ads (most are not), then optimize your listing for keywords they aren't running sponsored ads on, and run amazon sponsored ads. Your listing will then slowly rise in organic rankings from people buying off your sponsored ads.
We have over 50 PL products and have done this over and over again and it works great.
Hope that helps!