Hello and welcome,
Its a great set overall, one of my favorites. Its a really hard exhibit set to complete because a few of the cards are very hard to come by. I have been working on mine for over 6 years and I still need 25% of the set. Many cards from the set were produced every year and are pretty common, like the Waner Portrait. Others made it in 2 or so years and are 2-3 x harder than the common cards, the Waner Batting Photo would fit this. Then you have a few that were only printed for a year or less and they are very hard to come by maybe 8 x 10 times harder than the commons, these include a few of the variations, a few single players and all of the Plain backgroup cards, the Waner Batting Plain version is an example.
As far as overall pop there are not a ton of these cards out there and some will never have more than a 20ish card pop. One thing to note PSA is horrible on labeling the variations in this set esp the plain vs photo cards so dont put too much into the pop report as I have seen as many errors as I have correct cards for many. I would also venture to say there are still a lot of raw sets out there, prolly more than has been graded.
Here are a couple tough ones-
