Version 126.96.36.199.1 of Paid Memberships Pro is out with a single important bug fix for PayPal Payflow Pro users. This bug has the potential to hinder sales, so be sure to upgrade.
If you do not use the Payflow Pro gateway, you do not need to update. Although you may choose to update to get rid of the notice in the WP dashboard. There are no other changes vs v188.8.131.52. You will be safe to update.