I am in the same boat as NY. I have Shorais on two bikes, so it's worth having the correct charger. Remember that if you have a problem down the track with the battery, you can then say to the manufacturer/distributor that you used the dedicated charger only to charge/balance it.
The Shorais are good for the first 12 months, with regular riding, but as
[email protected] says, they need the odd freshen up after that.
I have had no problems with either of mine, and the one on the Ducati is almost two years old I reckon. It has only been on the (Shorai) charger about three times over that period.
As to the down side of trickle charging conventional batteries with 'normal' chargers? The weakness with some cheaper models of trickle charger is that they can fail to cut off, which may then cause them to kill the battery.
Not worth leaving them connected for weeks at a time for this reason if you're using a basic 'cheapie'.