I bought a TRS-80 as a 14-year old in 1979. Commodore Pet, Apple II, and TRS-80 were the only real options. The Altair was an entirely different beast. Take a look at the Altair advertisement in the wikipedia entry and you'll get the idea: https://en.wikipedia.org/wiki/Altair_8800

Ironically that Wikipedia page states:

"It was the first commercially successful personal computer."