The difference is whether the detergent goes through your pump (upstream) or is injected into the water flow after your pump (downstream).
Since upstream (most consumer units) goes through the pump, you should only use pressure washer safe detergents that won't harm the gaskets & seals.
Downstream injectors can use harsher chemicals since they don't pass through the pump. (Although you need to be careful of overspray & runoff with the harsh stuff.)
The Ladder Saver will spray with either system, but will only be able to apply detergent if you have a downstream system, or use an accessory downstream siphon like this one:Accessory downstream chemical siphon