You are correct that information on how they differ is confusing. One reason is that the firmware has been upgraded on the 410, which is why it now has the same managerial functions as the 650, but a lot of information/advertising is outdated.
410: fixed antenna; public groups; managerial functions
550: replaceable antenna; public and private groups
650: replaceable antenna; public and private groups; managerial functions; larger battery; faster charger
The very confusing part is the public/private groups and I am not even sure if I understand them thoroughly. (I programmed multiple public groups into my radios and don’t use private groups.)
Let me see if I can clarify. Let’s suppose you run a retail store. You need radios for security, shipping, registers and management.
On all three models, you can program public groups called, for example: store (all radios), security, shipping, registers and management. They can all stay on their own public group (“security”), but any radio can go on any group and ask them to switch to the all-open public group (“store”) if, for example, you need to do a group announcement. Also, any radio can call any other radio individually.
With the 550 and 650, you can program them slightly differently. You can make the store (all) as a public group and then program each department’s radio as a private group, such as security, shipping, registers and management. The difference is that all radios are still open to public group (store) calls, but will also receive their private group calls on their respective programmed group without having to switch “channels.” Also, unless you have programmed multiple private groups into every radio, “registers” would not be able to switch channels to hear calls going to “security.”
Thus, the 550 (and perhaps one 650 for its management functions) would be a better choice if you want all radios to be open to wide group (“store”) calls all the time but also open to their respective private groups calls (“registers”) without switching anything.
All these groups can be programmed in to the radios right from the keyboard. You don’t need the CPS or the mini-keyboard. What the customer programming software (CPS) does it make it much faster to program multiple radios. Plus, the CPS or the mini-keyboard will be necessary if you want to program them with unique names.
Without the mini-keyboard or CPS, your groups are listed on the face of the radio as: “Public group1,” “public group2,” “public group3,” and the radios are “123456789,” and “133456789,” etc.
With the mini-keyboard or the CPS, the groups can be listed on the radio face as: “Management,” “Registers,” “Security” and the individual radios can be named “Store manager,” “Register 12,” etc.