helen s - crossfit also is pretty difficult to describe in terms of intensity/duration/aerobic activity. The best answer to your question is "yes".
There are some workouts where you do 10 different activities for 30 seconds each, 5 seconds between each one, rest for 2 minutes, then repeat the whole thing 10 times or so. The goal there is to do as many pull ups or push ups or squats or whatever as you possibly can for that 30 seconds. Those are pretty intense, but you're working for speed so the weights are all body weight or less, so it's not so bad but it's fast enough that pacing is difficult. If it's recorded (sometimes is), it's harder, because you're shooting to break your PR. It's unlikely to toss cookies after that.
Then there's the workouts where you do a set number of reps, say 3, at the max weight you can possibly do 3 reps, for like 4 sets (or one rep for 5 sets). The point is to reach max weight in your 3rd or 4th set, you may not be able to actually complete the 4th set at the weight you chose. Those are NOT aerobic at all, and are boring unless you've got a PR you're shooting to break (even then, it's not exciting). You won't toss cookies after that.
Then there's everything in between.
The point is that, over a few months of 6 day cycles, you won't repeat a workout (no boredom), and each workout works on one or at most two of the four goals: agility, strength, endurance, and speed. Crossfit attempts to get it all in, just not on the same day. It is all scaleable, but the point is not to provide something easy to do before a vigorous bike ride. The point is to push you to your personal limit, wherever it may be that day. The trick is to plan adequately for the bike ride after, something made easier as you gain a better understanding of your personal limit (which, theoretically, is also moving).
Mick - you can totally do crossfit without tossing cookies. I never even came close to throwing up when I did it. But if there's stuff in your tummy and you're pushing yourself to the physical limit (in an attempt to move that physical limit out a little bit more each time), you're gonna hurl. You're asking your body to choose between spending the little energy you left it digesting food or healing muscles and connective tissue - healing will likely always win, which works out nicely since food is so darn easy to find that may be the point of the whole activity anyway.
Speaking of connective tissue - muscles improve fast, connective tissue slow. As you get into this, listen to your joints extra, extra hard. Use the granny gears, save your knees, back off the squats if you have to. You ARE improving just by trying, let everything catch up. I don't think you're the type to destroy yourself, but just in case. If you wait for a persistent twinge to bother you, you will regret it. If you're using advil or ibuprofen regularly to help get you through the "48 hours of soreness", back way off for longer than you want to. Repetitive stress injuries are the most obnoxious things on the planets. My mother had to stop dancing for a year and almost landed in a wheel chair because she didn't let her bones catch up to her new hobby, and didn't listen to her body because ibuprofen worked so nicely.
this makes me want to go do kettle bell squats.