JM is brilliant - I did 30 day shred and ripped in 30 back to back, 60 days in total and the difference was amazing! I did it in time to hit the beach last August! I plan to start up again in a few weeks.
JM is fantastic but also pretty tough, try it and see how you go but go easy on yourself, you may find lots of walking pushing buggy or carrying baby in a sling would be best for a month or two or 8 while you are presumably sleep deprived (and bf?). Enjoy your baby, plenty of time to get fit, not so much to cuddle a gorgeous newborn .
Tabata-very high intensity interval training. Extremely effective but absolutely brutal, to get the effect you have to work at absolute maximum effort for each 20 second blast. Even the fittest people feel like throwing up or passing out by the last couple of sets (that girl looks v fit but is not working flat out, sorry). So don't try it unless you are very fit to begin with. Due to its intensity you need recovery time so you also shouldn't do it more than once or twice a week, as part of a fitness routine that includes other stuff.
If you aren't very fit (but are reasonably so) you would do better to do a longer session of intervals a few times a week: say high intensity (80-90% effort) for 1 minute then reduce to 40-50% effort for 1-2 mins repeated for 12-20 mins. This will give fantastic results, especially alongside regular resistance training. This does form the basis of JM's Shred.