Mongoose is a semi decent brand, wiki it, not a wall mart bike, and it shows in the specs.That mongoose bike would be much better than a used Giant Cypress DX , believe me, cant go wrong with full steel rigid frame and fork, v-brakes, just one gear in front, a simple mountain derailure system, 26' aluminium wheels, it is the kind of bike that you can take to a neighboor bike shop in the thirld world and get it fixed for cheap.
Besides it has fenders wich are a big plus, if you dont want to stop when the weather is moist.
Ebay/craiglist old bikes are fine if you have lots of spare parts, experience and some money to rebuild them how you like it, but it is just a bad idea to buy one and take it right away in tour
Besides any bike you take will crap on you after couple hundread miles if you arent willing to maintain it.