The personal transponders are approximately 3/4" x 7/8" x 1/4".
They will work with AMB20 systems, older than that I don't believe they will work.
The older AMB sytems will only recognize the last digit. The last digit and any car number must be the same. If you are using any sort of bump up at your track then the bump up number and the last digit must agree if using the older AMB systems.
If you have purchased the newer AMBrc system the only thing you need to do is watch the race.
As far as weight, they are roughly half the weight of the rechargeable transponders used by most track, approx. 3 oz.