Both practices are a mixture of acupressure and massage. Acupressure being the application of pressure into the body at "tsubo" or "acu points". The same points into which Acupuncturists insert needles.
Seated Shiatsu is a mode of Shiatsu that is particularly suited to short sessions in working environments.
At first sight, the kneeling chair often used by shiatsu practitioners, appears to be at a disadvantage to the On-site chair. The On-site chair providing far more support for the client, enabling them to relax. However, this apparent weakness is actually the kneeling chairs strength.
Some days, however, people just want to abdicate all to their practitioner for a little while. The On-site chair excels at this. The On-site chair also enables the practitioner to get more body weight behind their acupressure.
In conclusion the kneeling chair creates far more interaction and as a practitioner I find this a big advantage, however this is not always what the client wants.