Yes, this is a great tool. I've been using Flightradar24 for many years now and am happy to pay them $3.99 per month for the premium service (gold - there is also a cheaper silver level and a free basic level). I have the apps on my iPhone and iPad and can set a custom alerts. For the most part, if the aircraft has ADS-B out (mandatory for some in 2020), it should show up. I use it when flying a drone to keep track of helicopters since they'e really the ones I need to look out for at the 400-foot level. If I see on the radar a helicopter circling around, I know to avoid the area until they're gone. This works most of the time, some aircraft do not show up. To date, no military aircraft have shown up on my screen, or govt. aircraft, for that matter (often have DHS helos transiting through and Navy jets coming into to get repairs at Boeing - they never show up).
It's one of my most used apps. I love it. Thanks for the link.