Hi there.
At this moment I would advise to wait for X-Cart 5.4 which is schedule to be released in about three months.
As for this particular 5.3.3.7 -> 5.3.5.5 upgrade, it makes sense to go for it because of compatibility with PHP 7.2 and redis
IN CASE you are running your store on an HDD.
Performance boost will be notable.
Also, there is a changelog available here:
https://devs.x-cart.com/changelog/5.3.5.5_-_10_jul_2018.html