As with ALL work outs it has to be taken with a grain of salt. ALL workouts are aimed at a general population model. a Man of say, 150-175 lbs, average weight average height and average build. These kinds of workouts are made so your advanced athelete can pick it up and take their body to the next level. i have a buddy out here with me who's doing the 300 workout, he's in pretty good shape like most army guys but it still leaves him wiped every time.
An excercise routine or workout is exactly what you put into it. if you always give it 100% all the time you'll get peak benefit off anything. It's a nice goal and if you can do this it'd leave you in very good shape but... it's almost always better to go to a fitness professional, have them do a fitness asessment and establish where you're at now, where you want to be and how to get there in a healthy way.
Nutrition plans are more important than all the pills powders and drinks in the world. Counting calories is an ok way to do it, but i find that too tedious. Personally, i find if anyone makes a plan to eat healthier and wants to do it, all the materials are available to them. Don't eat more or less, just eat different or work longer and harder. Almost all of the basics of healthy eating are out there in common knowledge. eat more fruits and veg, cut the fat out of the meat, try and keep the carbs in sync with how much you do. make sure you get your daily totals of vitamins, and try to even go overboard on certain vitamins. Vitamin C will buffer your immune system and help your body repair. make sure you get potassium to help break down the lactic acid in your body to keep you from getting stiff. little things a fitness expert can help you with.
For some people, and some body structures you may never reach that goal of looking like a walking tank, A fitness expert or a physician can help you determine what kinds of workouts will benefit you most in muscle growth and in muscle strength. I worked out a good plan with my local base health staff which includes a good dose of cardio in the morning and a proper weights plan at night.
I tried the 300 workout (the original one) with my buddy and we both finished in about 28 mins (those floor wipers are murder). It's an intense workout but it's not the right type of workout for me. it just doesn't focus on the muscles i want most.