The Spencer apple is a Yellow Delicious x McIntosh cross. I've never had it but it's said to be a good eating apple. The thing is, apple genetics are not simple, both parents are the complex result of random breeding, so your seedlings may be like one or the other parent, like the Spencer, or something completely different.

Sometimes the offspring has traits that are not like either parent. For example, yellowish Rainier cherries were a result of a cross between Bing and Vans, which are both red. In general, a chance seedling will usually have inferior fruit quality to that of it's parents, but sometimes you get lucky and the seedling will combine the good traits of both parents.