I think Billat's 30-30 intervals are more sound than Tabata's.

Though Billat's intervals were done at vVO2max in runners, I believe that's analogous to power output in cyclist. Billat's would rule out any confusion in power, or % power.

Normally, for cyclist 8 minutes is said to be the duration. So, 30 seconds put out your 8-minutes power. Then, for 30 seconds "float" at 50%. And repeat until you can no more.

I do it all the time.