Do ab machines work?

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.