True, you can eliminate all opportunities of leak except the tank seam by employing internal filters. But most internal filters are ugly, and sponge filters are the worse. There is, however, a poret foam design that I like marketed by this company:Or, just use an internal filter, then you only have the tank itself to worry about.
http://www.swisstropicals.com/library/cornerfilter/
I fully understand why majority of the plant folks prefer canister because of aesthetic, and silence. No other filters can even come close to competing with canister in those aspects. I use HOBs as a compromise with safety concern first. I tried to hide the intake pipes with plants but it's no perfect solution. HOBs can still leak or overflow, but with no external plumbing (only external box), the opportunities to leak is far far less than canister that has O-rings, clamps and external hoses. Adding an in line reactor, particularly DIY type, is more opportunities to leak. I have read enough leak and flood accidents of canister that scare me from using it in my living room.It doesn't do the "living art"-part any justice if you have internal filters or HOB (which can also leak by the way... ), internal reactors or any internal plumbing imo.
Clearly visible equipment doesn't really enhance the look of any tank for me.
I can't really enjoy a tank riddled with in tank equipment so it's not even an option for me, ever...
I have canister filters (5 atm) with inline equipment in my living room for years and never had any leaks.
For me canister filters and such hold the same risk as a possible leak in the tank itself. (Or a HOB cracking and leaking...) It's part of the game...
And let's be serious: it happens rather rarely provided the proper material, good care and caution so why compromise?
.