There's alot of naysayers out there that don't understand T5HOs... if you would have got that pos 2bulb single reflector for both bulbs coralife fixture, I would have said no.. don't keep any corals or clams lol...but you got a good fixture which can keep anything under it granted your water parameters are good.
you'll be fine...
Ask him next time if you need to upgrade your "fluval 405" to a bigger eheim canister filter next time for your 10gallon so you can get more flow and see how he reacts..if he just tries to sell you crap, then you know his true intentions and intelligence lol...
p.s. a fluval 405 would blast everything in the tank LOL...