The A1000 line has a metal case, while the A158 has a resin case that is chrome plated. They might be a different size, and they have different specs for weight and battery life. The A1000MA is kind of a buy-it-for-life-grade version of the A158 that recently came out.
https://www.casio.com/us/watches/casio/product.A1000RCG-8B/