I've been a flight instructor since 1991, but only taught for about ten years before moving on to Part 135 and airline jobs. It would be correct to say that I'm very, very rusty with respect to general aviation operations, especially that "VFR" stuff. I have managed to keep my CFI current by doing a FIRC every two years.
A few years ago, there were a couple of in-person FIRCs being taught by designated examiners. I've attended two of these, and they were really useful. It was extremely educational to hear about common checkride errors - what students tended to be weak on, and how instructors could do a better job preparing applicants for practical tests. In my opinion, these were the best training courses that I've attended, and you could also network with experienced instructors and DPE's.
Regarding online FIRCs: I've generally used the Gleim CFI renewal, but decided to try the King Schools version this time. I started around March 1, and have just finished up the last unit. Here's my comparison of Gleim versus the Kings:
Both FIRCs cost about the same ($129).
Both FIRCs are heavily "outline oriented". I thought the King course did a better job of emphasizing important concepts.
The Gleim course tends to be the easiest to use if you have a poor Internet connection, and it's easy to download the study units for later review. The King course has links to a number of articles and videos. There were a couple of times (in hotels) where I had to reduce the resolution of the videos to get them to play properly. I was on an iPad, so the lower resolution wasn't a big deal. Most of the time it's just John or Martha talking anyway.
As noted above, a FIRC must be at least 16 hours long and cover certain required topics. I get that. So some of the material was repetitive, and some was very good. I especially enjoyed the first two units in the King course ("Identifying and Changing At-Risk Behaviors" and "Using Scenario-Based Training"). This is just as applicable to airline training programs as it is to general aviation operations.
Both Gleim and King have excellent customer service. I got my temporary certificate almost immediately.
Finally, completing the King course gave me a whole new respect for John and Martha as educators (I did not use any of their material during my long journey from student pilot to ATP). Some of their early aviation misadventures are cringe-inducing, but they survived and told the rest of us "what not to do". Pilots tend to be intelligent, goal-oriented individuals. Sometimes this can lead to bad decisions when reality gets in the way of our goals. Starting to think about flying as a risk management exercise becomes a satisfying challenge and improves our own safety and the safety of our passengers.
Fearless