OS Engine Review

I have brought some OS engine from swanghobby.com and seems it is very good and low shipping cost from Hong Kong.
OS Engines

First to introduce a mass-produced 4-stroke engine, an innovator in every phase of R/C engine production, O.S. also retains a tradition of craftsmanship that pays off in durability and power. Each new engine is the product of over two years of testing and design—and more than two generations of R/C engine experience.

I have brought a 91Hz from swanghobby.com

With back-to-back FAI world championships in 2005 and 2007, the 91SZ-H was a winner by anyone's standards. Now there's the 91HZ – a 91SZ-H redesigned with the help and advice of the world's top pilots. It offers the tuning ease and performance consistency of the multi-time world champion and design innovations that promote improved cooling, a tighter compression seal – and tuning ease!
The narrow profile of the heat sink head helps the 91HZ fit completely inside cooling shrouds without cutting or losing cooling power!
Two heat sinks – one on the head, another on the crankcase – allow airflow to carry away heat and maintain performance.
Better overall balance reduces engine noise and promotes smoother, stronger performance.
The new 61B carb takes consistency to the next level. Dependability features start with an insulating ring which prevents crankcase heat from affecting carb settings. A generous use of O-ring seals – two on the main needle, one on the rotor – prevents air leaks and power fluctuations.
In-flight control of the needle valve ensures smooth, consistent runs.

http://www.swanghobby.com/osengine-fs-91sii-4-stroke-engine-pr-1618.html

O.S.ENGINE MAX-50SX-H Ring Hyper 2 Stroke Engine very good.