Small-cap exchange traded funds have quietly returned robust gains this year but some investors pass over the ETFs due to lower asset levels or thinner trading volume. Yet potential investors shouldn’t write off small-cap ETFs solely on liquidity concerns.

The Guggenheim China Real Estate ETF (NYSEArca: TAO) is this year’s best performing China-themed ETF, gaining 40% so far this year, but many overlooked the fund based on the fact that it has $46 million in assets under management, writes Brendan Conway for Barron’s.

The story is similar with other below $50 million small-cap ETFs, like the $8.8 million RevenueShares Financials Sector Fund (NYSEArca: RWW), which is up 23% year-to-date; the $25 million PowerShares KBW Premium Yield Equity REIT Portfolio (NYSEArca: KBWY), which is up nearly 18%; the $4 million SPDR S&P Mortgage Finance ETF (NYSEArca: KME), which is up 24%; and the $16 million IQ U.S. Real Estate Small Cap ETF (NYSEArca: ROOF), which is up nearly 21%.

Many financial advisors have steered clients away from funds with less than $100 or $50 million.

“You don’t want to go into a dark theater that doesn’t have any exits,” Dryden Pence of Pence Wealth Management said in a ETF Roundtable, arguing that investors should avoid funds that could shut down or pose problems if one needs to sell off a large position quickly. [ETF Liquidity is More Than Just Trading Volume]

However, the common notions of liquidity can not be associated with ETFs since the funds are only as liquid as their underlying securities.