The sportster is more of a third plane. Keep in mind that things like the 4* and Tiger are good second planes ONLY for some people in some situations. Generally a shoulder wing plane or a high- semi-symetrical wing plane is recommended for a second plane. Something like the GP Easy Sport, Goldberg Falcon, Avistar, etc.

Stepping up to a low wing plane is a big step, it's just that there are a few low wing planes that are more forgiving than others, like the 4* and the Tiger.