Smaller freewheels TEND to be weaker than the larger ones. That is, a 13/14 tooth is often weaker than a 16 tooth model. But, Odyssey has put a lot of reasearch recently into making very high quality product that stands up to actual riding. I would be willing to give it a try.
Just keep in mind, if you already destroy 16 tooth freewheels, then you probably won't be happy with a 13 tooth model. Also, you must have down drive on your hub or a flip-flop hub. (down drive accepts freewheels under 16 tooth)
The reason for a cassette over a freewheel is because the hub can be really strong and still be small. But, if you aren't detroying your current freewheel, the 13 tooth may last you a couple of years.