Just on those ADS-B transponders, yes, there are ADS-B out transponders, and yes, there are ADS-B receivers, however different manufacturers have different feature sets and it is worthwhile comparing them in depth before you spend your coin.
I fly behind Dynon in the RV and have ADS-B out using their transponder for 10 years with good results, however their ADS-B in system doesn't announce azimuth or range to an identified threat, it simply announces "TRAFFIC!" in your headset and leaves it to you to find the intruder and determine their 3D position in space and where they're going. To that end, I am leaning towards Garmin's G3X, or at the very least, a Garmin GNX375/GTX345R transponder as part of the upgrade for the new chariot. The reason for that is it provides better alerting by way of announcing “Traffic, 10 o’clock, same altitude, 2 miles" - straight away, that tells you where to look without having to go eyes-in to determine where the intruder is. Even without traffic displayed on-screen, you're alerted to where it is, the screen will tell you what they're doing (climbing, crossing L->R, etc).
This sort of functionality is not cheap, a Dynon transponder goes for around $4,500AUD, a GTX345R for $10,500 and a GNX375 for nearly $15,000, but if you need to upgrade to a C146 GNSS anyway (I do!), then that offsets some of the cost, a GPS175 is $10K, so between that and a Dynon transponder, vs a GNX for $15K, the difference is about 1AMU. I'll gladly pay that to have spoken traffic alerts.