We were gifted an Angelcare monitor from a very generous friend when DD was born. I didn't want one, but dcided to give it a go when it arrived.
We have a Tutti Bambini beside crib as well- for the mat to work you need to track a wire from under the crib mattress to the ground. There's no hole in the bottom of the Tutti to feed through the wire, so short of butchering the crib it jst wasn't going to work.
I had a look at the instructions and to be honest it seems like a bit of a faff for no real benefit- as other posters have said, they don't prevent cot death, they will only alert you when it's too late. There's actually suggestions that they're counterproductive, as some parents can become more lax with the safe sleeping guidelines because they believe the monitors will protect their child against SIDS, when really it's just a monitor. As others have said here, some parents have found that it actually makes them feel more anxious as well.
In addition, you need to be mindful that every time you pick baby up, you need to knock off the unit as it'll start screeching when it doesn't detect any movement.
its just immoral how these things are marketed as the pinnacle of safe sleeping, anti-SIDS technology when the only real benefit is "peace of mind".
Save your money, OP- stick to the safe sleeping guidelines (you're mostly there if you're intending on using the side car cot for at least six months)., they're much more likely to prevent SIDS than any fancy monitor.