Hello Catherine Tran,
No, you have to do the work. Haha, just kidding.
If that is what gets you to exercise, then okay. Otherwise, there are numerous exercises to work your abs, just as well if not better, without ab machines. This is a personal preference.
Depending on the machine, there are positives and negatives, just like anything else.
You may want to do your homework before using and/or purchasing something in order to reap the benefit you are striving for.
There are multiple ways to target the core: circuit style machines, free weights or bands, etc, Pilates style movements, with or without portable resistive devices, or on Pilates equipment, or traditional crunches.
I think what you use and when you use it will vary depending on fitness goals, level of experience, etc. By “as good as” do you mean “as safe as”, or “providing more strength more quickly”, do you mean “providing more muscle activation for more of the muscles of the core”, or do you mean “gives a 6 pack look more quickly”?
For example, I personally do not do pec deck butterflies in most machines as I am short and I find even with a pedal to release the weight I get some shoulder impingement. I do like to do floor Pilates with the addition of extrinsic weight, in the form of hand weights, or small balls, etc. I have seen some research that suggests that this is a good combination. If I were working with someone with a health restriction, or with a competitive athlete my answer might be different. The further you progress the more measurable differences in outcome in any choice of tools will matter.
Also, remember it is not the case that you must commit to just one. It is also great to have more than one tool in your tool box to target a particular area. It helps avoid boredom, keeps motivation high, targets muscles and accessory muscles in different ways, and provides a neuromuscular component.
The best way to tell is if you “feel” it in your abs when your doing the workout. If you just get back pain or a soreness then you should probably switch to a different exercise.
I prefer more functional movements than the typical isolated movements that machines limit you to. Especially if you are not a beginner or someone with some kind of an injury or other limitation, I would stay away from them as much as possible. There are so many other variations of abdominal exercises which you can perform that make machines obsolete. If you are looking for more resistance while doing your abdominal moves, use a medicine ball, kettlebell(s), DBs, sandbags, free weights, etc. Also Turkish get-ups are great for core stabilization and strength (among other things).