OpenType Font Tester is very easy to implement, after uploading he fonts, it is a matter of adding a single line of code (
iframe) to the client's website. Client has partial control over the appearance of the tester and which OpenType features are offered for testing.
Annual licence costs €200 for up to 10 font families (or 60 single fonts), €275 for up to 20 font families (or 120 single fonts); €350 for up to 35 font families (or 210 single fonts); €450 for up to 50 font families (or 300 single fonts); €600 for up to 100 font families (or 600 single fonts).
If you need higher flexibility in implementation, there is also a possibility to use API implementation, allowing full control over the appearance of the tester, access of multiple font instances and manual control of all paramaters. You will have to design your own user interface before the implementation. There is an additional costs for using API method.