My two cents: experience with several timing systems has lead me to the conclusion that the best of them all as far as accuracy is concerned is an experienced Time Machine operator in conjunction with gun time. Of course, this assumes the finisher is wearing a bib and the bib is visible to the select timer. It assumes that the finish density is low, such as in a small marathon or ultra.
All RFID timing systems have limitations. When properly used, Ipico, Chronotrack, and Jaguar have all performed well in races I have been involved with. Jaguar works best for small events. Ipico and Chronotrack can handle any size event. All will miss some tiny percentage of chips at either the start or the finish for myriad reasons.
Dual foot chips create the most accurate RFID results, IMO. Few races go to the trouble or the expense. Ipico and ChronoTrack bib chips are so sensitive that they require measures to keep spectators who are wearing bibs away from the start and finish lines - as, 15 feet or more, or behind a solid barrier. Using these chips with RunScore nevertheless produces accurate results when multiple mats are properly placed on the start and finish lines. With Bib chips, it is essential to employ "Last Seen/First Seen" technology either in RunScore or in the reader settings.
There are several other factors affecting accuracy and reliability. Some can be controlled by timers, and some require users to take some responsibility for using the chip properly.