Hi Jasper,
I would like to give some suggestion from my side.
1. The scale factor that you use is right basically. The typical sensivity is 16mV/g @ 3.3V supply for ADXL001-70. But the part by part difference may cause the sensitivity change a little, normally it is limited in +/-10%. You need to consider this error. So does any other sensor unless it is calibrated part by part before shipping to customers.
2. It looks like the core sensor is sealed in metal for the other vibration meter that you used. The sealed metal is just like the mechnical filter, so the acutal vibration is attenuated when it seen by the internal sensor. I worry about this may be the reason for why the other vibration meter output a relativley lower value.
Hope these can help.
BR
Neil