How to choose between a Doser grinder or a Doserless one? To do this you need to look at the operation of the two different models.
A Doser is a chamber that collects the ground coffee into a container.
A Doser chamber is divided into pie shaped segments that rotate with the pull of a lever to usually deliver around 7 grams of ground coffee. With each rotation a new section will move over the dispenser chute and deliver a pre-measured amount of ground coffee directly into the filter basket. This operation is found in commercial espresso grinders. The advantage of the Doser grinder is that it delivers quick pre-measured dosing which is useful in high volume environments.
For low volume situations the Doserless grinder may be the better option. For the Doser grinder to work correctly the chambers must be full. If you are planning on only making one or two espressos then the unused ground coffee sits in the Doser container going stale, which in effect defeats the purpose of grinding fresh to begin with.
With this rationale the Doser grinder would seem no good for home use; however there is a trick used by many baristas that can help eliminate the waste during periods of low volume use. Baristas will grind only enough espresso coffee into the Doser chamber for the shots they are going to serve. They will then use several successive pulls of the lever to clear the chamber into the portafilter, creating a mound of cofffee grinds in the filter basket. This mound will then be levelled off with a quick swipe of a finger or a flat blade. For high volume usse, such as home entertaining the machine can be switched back to the normal doser operation.
A Doserless grinder is just as it sounds. Coffee is ground and exits the grinder through a chute and directly into the portafilter basket. You would either attempt to grind the exact amount of coffee for that serving or you would overfill and level as discussed above. If you always overfill and level then the Doserless grinder seems to make more sense - however some people prefer the feel of the Doser grinder better. if you prefer pre-measured doses and frequently entertain or have a higher volume environment, then the Doser grinder is probably the better choice.
Either way - each grinder has its own benefits and can work when using the above tricks of the trade.