I have several of the surface extractors (SSE), but only one installed at the moment. If I have a tank that routinely develops a surface film, I'll install one and use it actively only as required (normally less than an hour of surface extraction per day is generous). But they do require a bit of DIY to be able to prefilter the regular intake for non-surface skimming operation (my canisters are all prefiltered bio-only similar to Jim's). There is a separate control for the surface skimming portion of the device.
The SSE is very prone to clogging if there is any plant debris generated in the tank, or small floating plants (duckweed, etc.) or snails. It is also a bit demanding of a relatively constant water level in the tank- it does autocompensate a bit, but not as much as you might like. The on/off control for the device can interfere with a cover glass as well, depending actually on the tank size (smaller tanks with narrow trim are a more likely problem, large tanks rarely). But for intermittant use, it can fill a need.