Is there any difference between them besides the form with -e being more formal?
I would say: No
Here in southern Germany you typically leave out the "-e" when speaking.
But leaving out the "-e" at the end of words (not only verbs) and even names (!) is typical for the region where I come from.
But this has nothing to do with being formal or non-formal. It only has to do with speaking dialect or speaking Hochdeutsch (official German).
For some verbs (for example lass/lasse) I was even convinced that the form with the "-e" is wrong - until I looked up a dictionary that says that both forms are valid.
(Please note that there are verbs whose imperatives which never end with an "-e": Nimm for example.)
Are then both forms, with and without -e valid and correct?
I looked up some verbs in the dictionary: For some verbs the form without the "-e" seems to be valid, for other verbs the form without the "-e" seems only to be valid in spoken German.
You'll have to look up a dictionary to find out if the form without the "-e" is valid for a certain verb.
By the way:
In older texts you'll often find an apostrophe whenever an "-e" at the end of a word has been left out:
Geh' bitte weg.
Pack' mit an.
Zeig' ihm unsere Wohnung.
Ich will nur meine Ruh'.
(In the last example an "-e" has been left out at the end of a substantive.)