This does get us to Yang Zhenduo's statement:
"Whether you do Chen style or Yang, or the two different Wu styles or the Sun style, they are all different. You can say that each one is unique, that they are all different.
In China, there are different tastes: sweet, salty, sour and spicy. You may say spicy is no good, but all the people in the south have to eat spicy food. People in the north, when they eat spicy food, all say this is horrible. So it depends on which one the practitioner likes. You say this one is no good, but I say this one is the best. So you cannot say which one is better than the other."
The different training systems are different. T'ai Chi Ch'uan itself is one thing, and you can do it or you can't, but the 5 main styles YZD mentions aren't the art itself, they are only ways of training your body and mind so that you can reproduce the art form physically. Moving your arms repeatedly through the P'eng motions dictated in the form is not T'ai Chi itself, being able to neutralize attacks consistently with P'eng is. So, all the masters of old could see that the other masters could actually do it, and were happy for them. They still, however, wanted their students to have to go through the system that they knew would work because they'd been through it.
Knowing their system well, I can say that if someone has (IME) worked with the Wu family and their senior instructors for 15, 10 or even 8 years, they should have enough to work on for the rest of their life. Around 8 years is the point at which a serious student becomes "self-correcting" in the Wu style, where the basics can then be applied to situations and they retain their internal consistancy. The family says that knowing the basics that well is like gold, you can hammer it, melt it, break it, but it is still gold. You may study Yang style out of curiosity, perhaps, but not because there is anything missing at that point.
The families don't train the same way; P'eng is P'eng, but how they get to P'eng is different. Training different styles can be a problem if, when your Yang style instructor is expecting you to work on his "Grasp Bird's Tail" you are working on Eddie Wu's or Wu Ta-hsin's (they are different) or Cheng Man-ch'ing's or whoever's. From an instructor's point of view that is "teacher shopping," mixing and matching and behaviour that is very common in the West (people don't even know that they are doing it), but it doesn't inspire a good teacher to go out of their way to show more things to the student who does it. The traditional teacher/student relationship isn't very well understood anymore, for many reasons, and isn't enforced the way it used to be by the families, including the Wu family, but you can bet your last deutschmark that they are paying attention to who is doing what! A good T'ai Chi instructor can tell just by the way you walk and move if you've been getting somewhere with your training, if you've been working on what they've shown you. They can also pick up the flavour of another style right away, too. So, there are no shortcuts. If you are training now with the Yang family, you owe it to them to consciously forget about what else you've learned. It is a different path, Yang Ch'eng-fu famously changed the form that he learned from his father, uncle and brother, Wu Chien-ch'uan changed how he taught what he learned, Wu Kung-yi changed it again, Wu Ta-kuei changed it again, and Eddie Wu has changed it even more. As much respect as there is, there is as much technical difference in training emphasis between the two schools, it is too confusing. Your body will remember some things of course, you don't learn this stuff with your mind, but what comes out should be a pleasant surprise instead of a conscious grafting of small circle onto large.
Anyway, that's just my advice, you can make what you want of it.