Yeah, I use FSRecorder for doing formation work. Sometimes it can feel laborious, while other times it can be done really quickly (depending on what you want). For instance, with the Mustang/jet screenshots, I'm still not very experienced flying formation with jets, so I knew holding position on the Mustang (that I prerecorded) was going to be a challenge, so I made the lead flight extra long (about 16 minutes - more chances for good screenshots) and kept it very stable, and with only very gentle turns and l made sure there were enough times of straight-and-level flight to make it easier in the jet to catch-up/adjust to the lead if needed. The challenge for me when it comes to flying jets in formation is the response (or lack there of) of the throttle/engine power, in which you never get as instant of a reaction to the airspeed via throttle as you do in the prop planes, which I'm far more experienced with flying formation. When it comes to flying formation with prop planes, from all of the formation flights I've done in the sim, I now can really get attached to the lead easily and hold it there through most maneuvers, changing attitudes, airspeeds, etc., with no problem, so for the Mustang/T-6 screenshot above, I just took the Mustang up for a 5-minute flight right over the airport (keeping the airpseed down to 160-mph), recorded it, and then jumped into the T-6, at the same airport, played-back the recorded Mustang flight, joined up immediately for a few minutes, and then played both recordings together to get the shot. One of the tricks I've learned from the real air-to-air photographers, when you're just trying to get some good screenshots, is to just fly circles in formation, that way you'll very efficiently get every possible angle of light. You wouldn't believe how many air-to-air photoshoots, especially in the aircraft/warbird magazines, are shot just flying in circles immediately over or near the airport they took off from, and all captured in 15 minutes or so.
Here are some more shots from the "Heritage Flight practice" (it should really be an F-16 rather than the F-35, as the F-16 is paired with the Mustang and the F-35 is paired with the P-38, but I don't have an F-16):

