The features field is NOT a value from the CCID USB descriptor. It is a field I added to indicate special features of some readers.
|features PIN Verification||39||15.35 %|
|features PIN Modification||36||14.17 %|
|features contactless||31||12.20 %|
|features ICCD||25||9.84 %|
|features Multi interface reader||14||5.51 %|
|features 2 slots||11||4.33 %|
|features Second interface||7||2.76 %|
|features biometric||7||2.76 %|
|features 3 slots||3||1.18 %|
|features 5 slots||3||1.18 %|
|features ExpressCard||3||1.18 %|
|features firewall||3||1.18 %|
|features 4 slots||1||0.39 %|
|features serial||1||0.39 %|
Some features can be extracted from the USB descriptor like PIN Verification, PIN Modification, ICCD, number of slot. But the other features are added manually.
A majority of readers have no special feature. It is not directly visible from the table above because some readers have 2 or more features at the same time. For example all readers with PIN modification can also do PIN verification. But the reverse is not true. 3 readers can do PIN verification but not PIN modification.
If you want to find readers with a special feature, like contactless, I recommend to sort the reader matrix by 'features' field. It is then easy to find the readers with the feature you are looking for.