I am wondering why you never see the (weighted) nominal value of the underlying assets of a bond ETF mentioned anywhere.
It seems to me this information is needed to determine whether a bond ETF is fairly priced, just like you need that information to determine whether a bond is fairly priced. All that is mentioned is the weighted NAV (net asset value) of the underlying, which is of course also somewhat important, but does not enable you to determine if the underlying was fairly valued in the first place.
This seems especially relevant since ETF share prices don't need to match the (weighted) price of individual underlying assets .
 the market value of a bond depends on its nominal value, duration, coupon rate and the current risk free interest rate. Example: when the risk free interest rate is 2%, a fictional 1 year US treasury bill with a nominal value of $100 and a coupon rate of 3% could be expected to have a market value of $101.
 Mostly to assure the buyer that there isn't a large gap between the market price per ETF share and the NAV
 Even if an ETF owns only bonds with a nominal value, and market price, of $100, the ETF share price could be fair at $23.36, because each share represents 2336/10000th of an underlying asset.