Agree with chip. For what you're doing first one will be fine. If it's only going to be used on track then chances are if you ever do roll you wont hit anything and the first cage will be substantial enough to protect you.

Sparco do a more comprehensive cage for about 300 quid so might be worth looking at.

2nd one looks nicer but would be over kill.

If you know someone who's good with a welder you could easily cut off the tabs for the rear cross brace and then weld in a proper cross brace. That would make it much stronger and wouldnt cost much. That's what i'd do.