This is kind of a funny question. Yamaha make a variety of upright models, which vary in price and their quality. The difference, IMO, between the cheaper and more expensive models is marked.
From what I can see the LU90 is an obsolete model which was one of their cheaper models. Made in Indonesia. If you find a good dealer they can explain the differences between a cheap model and the more expensive ones. The yamaha website gives quite a good indication itself of the differences, in a euphemistic way.
In this country their is quite a market in very good quality second hand pianos from Japan. I have a U3 of this type. Although it is old, 30 years now, I enjoy its tone and touch very much.