A friend of mine is using a can filter like that and it works just fine - I'm planning to do the same as well. Putting the filter inside the room takes up valuable space and limits your ventilation flexibility. For instance, I'll be venting two chambers through a single filter by using a Y fitting and an adjustable damper(for balance), then sending that through the fan, out of the room, and into the can filter.
Just remember to take the white prefilter off the outside and place it on the inside - you don't want to prematurely clog your carbon with dust.
Although you don't have much dust in the room because you're also filtering your intake air, right??? (hint, hint)
It should be noted that one drawback to this is that, since your filter will be running at a positive pressure(air is pushed into it) rather than a negative pressure(air pulled from it) that your duct connections will be more prone to failure. If they fail, you'll be spewing stanky air, possibly revealing your grow(I'm assuming you're a legal MMJ grower like I am, but you still don't want to attract thieves). My backup plan is to have an Ozium timed-dispenser helping to neutralize any stray odors that make it out of the growroom and into the surrounding environment.
