I think training treats are just like treats for us. anything is ok as long as it is in moderation and there are no allergy issues.
Just like you would not want your kid living on mars bars or mcd's food, you would not want training treats to be a major part of their diet.
So use whatever works for your furbaby IMHO
Melei's favorites are frozen peas and bits of lowsodium tostitos.
I also use those soft treats like snausages or bacon strips and I cut them into little bitty peices and put some in a ziplock baggie for training treats on the go.
Women are angels, and when someone breaks our wings . . .
We simply continue to fly . . .On a broomstick.
We are flexible like that.