Straight Eight is an heirloom variety. So all seeds you buy of Straight Eight, regardless of what company is selling them or if they have it on the package, are heirloom.

"Also, is it true that with heirloom plants you can keep the seeds from the fruits and replant them the next year and they will remain relatively the same?"

Heirlooms are open pollinated varieties (OP for short). What you said is true for all OP varieties as long as you keep them from being cross pollinated by another variety. If a variety gets crossed then it is no longer the same.

Rodney

P.S. Taste has nothing to do with being an heirloom. There are plenty of heirlooms that are non-edibles (flowers and such).