Shape is wrong
It is certainly not a usually seen shape for Paul Ysart crown weights. But it is an ok shape for some of his early ones!
Here's a pic of one owned by a member of the Paperweight Collectors Circle: http://i3.tinypic.com/wbyt1g.jpg
There is also a "squat" example shown in the 1969 Evelyn Campbell Cloak book of the Bergstrom collection (plate 33, item 494) and this is also shown (but top view only) in the later 1989 book of the Bergstrom weights. The acquisition date was May 1942, so it is pretty certain to be a pre-war weight.
base is wrong
The base finish on Paul's early weights does vary, such as: "crunchy", "small round button", "unfinished plain cracking off", "smooth polished", and a few other variations, too.
and the quality is not up to his standard for these.
This weight does appear to be a lower standard when compared to much of Paul's work. But I think the visual aspect appears less precise mainly because of the watery coloured elements around the red aventurine. I would agree that the way the canes do not all meet in the base is rather sloppy and would not be normally expected of Paul.
He never sold seconds either.
Maybe. Maybe not! He was known to sell items "out of the back door" and at local pubs, and I see no reason why some of those items could not include poorer quality ones. I know of a proven Paul Ysart weight, given as "payment" for work done in the factory, which is very poor quality and still rates in my opinion as the worst PY weight I have seen.
So, even with the reservations stated, I do think this is very likely to be a genuine Paul Ysart weight and probably from the 1930s.
What is very unusual is the flower on the top - instead of an air bubble. Although I can't be 100% sure it's a Paul Ysart flower (perhaps it could be a Salvador flower??), I have seen other PY petals that bear a reasonable resemblance to the ones in this weight.
I vote "Yes" for a Paul Ysart weight ... but with a certain amount of "hmmm? factor" thrown in.