Hardtop wasn't originally my idea; it was my wife's, but I've grown to love it and haven't felt the need to remove it.
Hot days:
Great when the Cobra is moving because you get air movement but without the sun's rays beating down on you
Not so great when not moving. I feel it traps heat.
Cooler days:
Great since you don't have a completely open top in cooler temps (air movement). I feel it helps with the seat warmers (probably placebo lol)
Trackdays:
Difficult to don helmet with Hans device (tight)
General use:
You deal with a fixed/inflexible hardtop when entering/exiting (driver height might be an issue)
Style:
A little different from the norm, catches the eye, and it's removable; there are different styles (backdraft fastback hard top - scalped in the rear, Le Mans or Fastback styles from 427hardtop, or FF)
Hope this helps. Overall, we've been very happy with the hardtop
Ours
Photo from Goodwood
FF Hardtop
427Hardtop (Left - Fastback style ; Right - Le Mans style)
FF with 427Hardtop - Fastback style