First of all, I am going to say something which is common among humans, and this is to imprint some sort of fearful, bad energy around something in their minds. This bias someone's perception around it, particularly when strong emotions are involved. This is something which must be avoided at all costs… for the light to flow correctly, i.e. to understand and etc.
What I mean with this is that if you are only accustomed to fairly simple unregulated “MOSFET” drivers, it may be harder for you to see this clearly, but it certainly is possible.
These regulated drivers employ a MOSFET to regulate or limit the current, using a sense stage to do this. They are fairly simple too, the only technical difference between a blind MOSFET driver and these regulated ones is the presence of a sense stage. Thanks to this sense stage they can precisely limit the current, and they can do it without PWM (pulse-width modulation).
I somehow sense that you probably feel that limiting the current is bad, but this is not. Without current limiting you could find yourselves with lower than expected output or damaged emitters due to overcurrent. Drivers which properly sense the current can take care of this. The problem I came here to discuss is that these “revised” SST40 drivers are using a coarser sense stage, with more resistance (the R020 versus the older R010), which is undesirable as it unnecessarily drops input voltage.
How did you checked that? :D The voltage difference or voltage drop between the power supply output's voltmeter and the driver's input terminals only appears when the current is flowing. The driver's spring also drops some voltage as it also has some resistance, by the way.
Remember what I said before, by Ohm's law V = I × R. If you use a multimeter and measure the voltage at the driver's input or at the end of the test leads without load, you'll of course get the same value. In these conditions the only current flowing is a veeeery small tiny bit of current which the multimeter needs to get its measurement done, but since it is so tiny the voltage drop in the power supply leads and connectors is also insignificant. However, let the current flow and you'll see. This is the reason I said “hire some assistant for him/her to peek right at the driver with the probes of a multimeter”, this is because when you are connecting the PSU probes to the driver with your hands and you “close the circuit” so current is flowing, you may need someone to put the multimeter probes above the driver ring (negative) and somewhere in the spring. You will then notice a difference: the larger the current flow the larger it will be.