Personally, I would not use low-volume ETFs for a couple of reasons.
First, if you are using a limit order (and you should be) there is really no enough action for a trade of 500 to 5000 shares. You just don't get execution. I would prefer an ETF that trades on average 100,000 shares a day minimum.
Second, low-volume ETFs are always in danger of being shut down by their sponsors.
But SCHA averages more than 100,000 shares a day, so it is OK.
And a related blog article on this to read: Schwab ETFs Struggle in the Shadow of Vanguard - Forbes