Alternative to Finis Tempo Trainer

I have been wanting to buy the Finis Tempo Trainer for quite a while. What is stopping me is the reviews I am reading on Amazon. These devices seem to be notoriously unreliable. They either come with dead batteries or last for a very short time.

So, I am wondering whether there is an alternative to this TT?

Or is it worth the risk to go ahead and buy the Finis TT?