There is quite possibly no advantage to using one of these compared to a bowl.

The measuring bowl generally available in the UK has, in my mind, some flaws for precise measuring, particularly of small koi.

1) the end slopes by approx 1.5cms top to bottom, therefore dependent on where you position the koi it affects the measurement. The shinkoukoi vessel has a straight end.
2) the scale on the side does not go from the top to the bottom of the bowl and there is no scale on the bottom. If you hold a small (up to about 35cms) koi to the base of the measuring bowl (where the scale starts from) then the bottom of the measuring scale ends before the top of the tail. Obviously this is not the case on the shinkoukai vessel.

I accept these are not major issues and not enough to warrant the cost of the measuring vessel at UK prices but are just a frustration. However, you can in reality adjust the length of a koi by 1.5cms with creative measuring.