Good enough for what?
This is a question that only you can answer for yourself…
If this question is for a 16 year old athlete, aspiring to win state, national and perhaps even international medals, then, of course NO…this is not sufficient… not by a LONG way.
For a middle-aged executive…maybe. But, there needs to be other workouts too…all, part of a fitness regimen. Which again, depends on the health/fitness goals of the individual, around which the training schedule needs to be drawn (either by the individual, if he/she knows what they are doing or by a Qualified Professional….important note: Qualified Professional does not mean someone with “Personal Trainer” written on their T-Shirt or even if they have a gazzillion Certificates, or even if they have six-pack abs… Just these are not in themselves, qualifications that will help you with your fitness/health goals).
For a 80 year old woman…NO… this is wayyyyy too much.
Anyway, planks needs to be done, with strict form and some variations are more difficult and effective than others. You need to do them with strict form and need to progress slowly.
So, what are your health/fitness goals? Make sure you can answer that… Then, depending on your answer, there are likely many different solutions (oriented to exercise, nutrition and life-style). When working out the solution, most appropriate, most liked by you, and one that you will be able to stick with, you (or a qualified professional) can then see if/how planks (especially those that you do for 5 minutes) fit into the proposed solution/s.