Not really a trade in program put in place.
They are set amperage units, so there are 15amp, 30amp, and 60amp units.
If you are only going to use it as a power supply, then you would look at the amperage draw your electrical system would be pulling with the car off at a car/trade show. If you are going to use it as a charger, then go as big as you can afford if you have a bank of more than 3 batteries. If you have a bank of batteries then you can basically take the amperage output available and divide it by the number of batteries. That will give you the basic amperage each battery is going to see during charging, so if you have 6 batteries and the 60amp IntelliSupply then each battery would see around 10amps each. If you had the 1005 charger and a bank of 6 batteries then each battery would only see around 4amps. Optimal charge rate is around 15amps per battery.