the shear stress of a single deadbolt is much higher than a person can kick (can hold the weight of about 3 cars). the advantage provided by the locks you posted is that the force is spread across 3 or 4 points on the door and frame. if you reinforce the frame/strike plate and door, a single deadbolt should be sufficient. then, you could use something like this:
http://www.amazon.com/Schlage-BE365VCAM619-Camelot-Keypad-Deadbolt/dp/B000NJJ1MQ
if you are still worried about strength, you could install two of them :P

Depending on where you live, a lawn mower of some kind is probably important.

Since everybody rightfully recommends changing the locks as soon as possible, I am also looking into getting some kind of keypad lock, at the temporary housing we were at it had one of these and it was ridiculously convenient to lock/ unlock without having to fumble for keys. I have read that since this particular model has a longer lasting battery since you have to physically turn the lock after unlocking (unlike the ones that move open electronically), plus with the keyhole you can still unlock it with a mechanical key in case the battery fails

Also a REALLY GOOD HEAVY DUTY TOILET PLUNGER

This one was in their keypad line -- BE365. So, the cylinder is really just a backup, in case the battery is dead or you forget the combination.