Products are similar.
Some facts that I know, may be it helps you:
-Explorer has cheaper SMS, more wide coverage, cheaper rate to mobiles, free web-based SMS service, also you have possibility to see your balance on handset LCD for free, starting package 49$
-Passport has voice recording feature, conference feature, starting package 69$
-really all TravelSIM based products including Explorer have 24 months expiration, not 12.
-Some months ago Passport had a continious problems with top up.
- other features for both products you can see on telestial web-site and you can ask their opinion too
