You won't need one on most tracks or autocross. Hard tops hold up alot better than convertibles when placed on their tops.
I wouldn't get anything without a cross brace and a harness bar welded in. You don't need it now, but when you need a bar, you will need a real one. One with a diagonal brace and a horizontal brace.
Check out Steeda, they have some 4-point bars that will bolt in (they can be welded too), still leave you use of the backseat, and they aren't that bad $ wise.
'94 Laser red 'vert. Still a 5-oh... for now