I did a custom install job for my Fluvals. I added 3+ feet of 5/8 inch vinyl tubing so I could put the canisters in the room behind my tank ( laundry room, spills dont matter there). I used vinyl hose connectors and metal hose clamps from Menards to splice the vinyl tubing into it. I have my inline heater between the tank and the wall, as I had left room so I could fiddle with things behind the tank. Even if your filter tubing is not the correct size, all you would have to do is buy a vinyl addapter to fit the different tubes (ie: a 3/4 to 1/2 adapter) and some vinyl tube to splice it in. But I would not worry. a 5/8 inch insert on the end of the heater will be snug enough on a 3/4 hose to clamp it water tight, and you could jam a 5/8 inch insert into a 1/2 hose with a little effort. Thus, the Hydor could be stuffed into anything from 1/2 inch to 3/4 inch. Which is why they say it fits most filters. I would bet all the filters are 5/8 inch tho.
Remeber to look at the online prices, as I am sure you have, since you said you are placing an order.
I like the Fluvals. I have no reason to say they are better or worse than eheim, rena, or cascade, since I have never had them. I have had a magnum, and think the Fluval is much better than the magnum.