The product you linked to there isn't a harmonic drive - it has a planetary / epicyclic reduction stage. It's possible there is less backlash than you currently have but there's no way to be certain unless you take a punt..

I made my 4th axis using a true harmonic drive sourced from a Korean machine breaker. When combined with a used Yaskawa servo drive I have pretty much zero backlash and 60rpm (3000rpm and 50:1). Perhaps a bit OTT for your application but it can be done without breaking the bank.