cant you try those pedals? i mean, they are not botique or anything, so why not go to a music store and try it? ... bring your guitar and your amp to be accurate... cause the sound you'd get from that 50 watt tube amp may actually be world's apart from your 20 watt solid state practice amp.
dont have an amp? ... then test your stuff in 20 watt-50watt and 100 watt solid state and tube driven amps in the store. at least bring your guitar OK? dont be lazy.
emplyees wont help you? ... count your money in front of them and say "i am CERTAIN i will end up with one of these pedals today, so help me god."
buying second hand and no way to test it? ... do the step i just mentioned in a music store and buy a pick on your way out while saying, "oh well, turns out both of them sucked, thanks for the help guys."