I also have the Summer one, its good but only suitable from about 21 weeks and sometimes heartbeat is hard to find. Have a look on Ebay, I think the Angelcare brand has got some good reviews. (sorry I don't know how to do links to it)
Thats great, good luck with the rest of your pregnancy. Your post reminded me to dig out my summer monitor for this pregnancy - its not really that good - very hard to find heartbeat but could hear lots of kicks and feel plenty of movement so I know everything is ok but would not recommend it to anyone.