For many verbs the additional "-e" in the imperative for second person singular is a question of regional dialect, personal preference and sentence melody, hence it does not really matter regarding correctness or understanding. For "handeln" you could say: "Handel!", "Handle!" or even "Handele!", for "schreiben" it can be "Schreib!" or "Schreibe!". This does not work for verbs that have an irregular imperative like: "Sei! or "Nimm!" and for some verbs that would end in a difficult to pronounce ending without the "-e". Like "wenden", you see that already in the "du" form: "du wendest" where there is already an "e".
I hope I could be of help.
quick is also an adverb, but it's not standard.
In British English it is an adverb too.