It sounds like you’re not exactly new to riding, and the allure of a sportbike is strong – understandable! Many riders eventually get the sportbike bug. You mentioned experience and owning an F2 previously, so you’re not coming in completely fresh. The jump from an F2 to an F3 is minimal, and you know these are generally good machines, though like many 600s, cam chain tensioners can be a point to watch.
However, unless you’re getting an exceptionally good deal on an F3, it might be worth considering slightly newer 600cc sportbikes. The newest F3 is still around 15 years old. The used market often sees F3s priced similarly to slightly newer models like F4is, 03-04 Kawasaki 636s, and 99-04 Yamaha R6s. While these aren’t brand new either, the slightly newer generation bikes often offer advantages in terms of technology and potentially wear and tear. That being said, a pristine ’95 F3 is always more appealing than a beat-up, newer R6.
Thinking about different riding experiences, at one point, I had a diverse garage: a Dyna with forward controls and ape hangers, a Buell with clip-ons and rearsets, and a Speed Triple. Interestingly, the riding position across these varied bikes wasn’t as drastically different as you might think. Moving to a sportbike, you’ll just gain an extra gear compared to something with pushrods from Milwaukee.
The real adjustments when transitioning from a Harley to a sportbike, in my opinion, are twofold. First, you’ll notice the rear brake on a sportbike feels significantly less effective compared to what you might be used to. Second, the power delivery of a 600cc sportbike is dramatically different from a Harley. A 600 makes its power way up in the rev range. “Linear” is definitely not a word Harley riders would use to describe the power curve of a typical 600cc sportbike. This high-revving nature can make them a bit more demanding to ride smoothly at first.
Ultimately, I think you absolutely should try riding a sportbike. There’s a huge world of fun to be had on two wheels, and exploring different styles of motorcycles is part of the journey. Give a sportbike a try and see if it clicks with you.