They are the same price, well made, and from excellent, established suppliers with great reputations in
vaping. [Although the Prodigy line (V1, V2, V3) has had more reliability problems than the one-version Silver Bullet.] I can think of
three factors to distinguish them:
1. Size and appearance: They each have a distinctive look. I believe that the Prodigy is a bit smaller.
2. Position of the switch button: The Silver Bullet's is on the side near the atty end; the Prodigy's is at the base. You would use different fingers to engage them.
3. The Silver Bullet is intended to be used with an 18650 ~2500 mAh 3.7V battery.* The Prodigy is designed for 6V vaping using two stacked 750 mAh RCR123A batteries or 3.7V vaping with a 1600 mAh 17670 3.7V battery.
* Many people do stack two 3.0V batteries in the SB for 6V vaping, but AltSmoke doesn't recommend it.
Watch review videos of each. Think about what
you want in a mod and them make your choice. You are unlikely to regret going with either.