The Alpina / A1 was Sinar's attempt to produce a lower priced camera into the hands of beginners.
Except for the rail, most things are similar to the F series. The rail is its greatest limitation. While the rail is technically 18 inches, it doesn't allow for the full length to be used. When using wide angle bellows and lenses, the rail can hit you in the neck, so you need to be extra careful. It's a Sinar, made as well as any other Sinar, Portraits with a 250mm lens would be perfectly doable.
The F/F1/F2 are far more versatile and easily upgradeable. I don't know the "reasonable" price you propose to pay for the Alpina, but I have an F listed for not much money, and my price includes shipping.
Kumar