First Name in subject line of email?

I've been putting prospects or existing customers/partners first names in the subject line of emails I've been sending out and have been seeing more responses. For example: 'Dave- How are you managing xyz?'

Yes it takes a little bit more time since you can't mail merge, but for the past couple of weeks I have been receiving more responses. Looking for feedback on if other sales savages think this is a best practice to keep on doing or if there are any negatives with this tactic.

Thank you,

-Salami