As mentioned earlier, the Rat, Scout and Photon Torpedo all have a similar pedigree, and it's hard to lose with any of them--they're all great, simple backups.
A couple of the advantages of the Rat/PT is that they are dual o-ring sealed, and some say the twist-on threshold is a bit less vulnerable to accidental depth-activation than the Scout.
Just in terms of price and availability, I'd try to find a used Photon Torpedo, else the $50 old style Scout.
A couple of the advantages of the Rat/PT is that they are dual o-ring sealed, and some say the twist-on threshold is a bit less vulnerable to accidental depth-activation than the Scout.
Just in terms of price and availability, I'd try to find a used Photon Torpedo, else the $50 old style Scout.