Brilliant for naps and monitoring play time for a child who is old enough for a little freedom. I love how my daughter has no idea how I know when she tries to jump on the bed! I've used it for naps in the swing from newborn on up and for naps otherwise.
We are on our third year with this monitor system. We've used it in two different rooms of a one level house. Both locations work equally well. I never use it outside, however, due to static. It just doesn't work well enough.
Shortly after we got this video monitor the volume dial became very sensitive and quirky and would only work well if tweaked to just the right spot. Basically, we have two volumes that amount to normal and loud. Those are the two choices.
The other tricky thing is that we have only a couple of sweet spots in the house to place the video display / sound receiver unit. If it is not placed in a very specific spot it will have a very noisy picture and static sound that would be way too annoying to even bother with. Thankfully one of our sweet spots is in a convenient place so it works for us.
If positioned correctly, the sound detected in the monitored area is very sensitive and helpful. The picture is ok, but don't expect to get a highly detailed, informative picture unless the camera is positioned very close to the pictured area. In doing so, you limit the area that is monitored visually which might be fine for a crib which I did actually use it for briefly right after we bought it. The way I usually use it gives me a general sense of where the child is in the room.
Bottom line for me is that I have had tons of use out of this video monitor system, as it is used daily. I've found ways to make it work for us. We love technology and gadgets but the truth is we haven't investigated what might be interfering with our units because we have been able to get around it.
If you already co-sleep, this can be a good tool for helping keep nap time safer, together with a completely safe baby proof, low level sleep environment and physically going in to check often as needed. I really like this co-sleeping book for anyone interested: http://www.amazon.com/Good-Nights-Parents-Family-Peaceful/dp/0312275188/ref=pd_sim_b_2
If you intend to use it for night time I would search and find the review titled, "Beware - No Security". That would give me pause if I were going to monitor night time sleep. But I don't yet so I am not as worried about it. Maybe consider buying from a place with a liberal return policy.
We received this monitor as a baby shower gift when we had our first daughter more than two years ago and we LOVE it!!! After being dropped many times, we decided to replace it now that we have another baby. We use both cameras, but they can interfere with each other which is why I gave it four stars instead of five.