Unfortunately, i had the same experience as alot of other reviewers before me. Decided to 'upgrade' my facebook store but that didn't worked out so well...
First of all your product photo's have to be squares, if they are not they will be cut off and this will look unproffesional on your facebook page. With the previous app this wasn't an issue.
Beside that, there is no way to order your products. Facebook decides for you how to order them and this seems pretty random (or probably with some fancy algorithms that none of us will understand).
On top of that, there used to be an option that customers were re-directed to your product page. When a customer clicked on your product in the facebook store, they were redirected to your website or the checkout page (there was an option for the admin to choose). Now they are being directed too the checkout page (either via facebook or shopify) and there is no option anymore for directing them to your regular product page. Pushing customers towards the checkout without even seeing your regular shopify store/website is too pushy for my opinion.
At last, and for some of you this might be no issue at all. There is no way to adjust the tab name. In the previous app we could think of any tab name that we wanted and just put out there mannn... Back in the days...
All in all: 1 out of 5, don't upgrade!