I don't work for SAP, I do work in the SAP space (which extends far beyond what many people perhaps realise). I do use OpenUI5 quite extensively, so these are my thoughts, coming from direct usage experience.

You're wondering if it was useful. For me, it is extremely useful. It's a toolkit that has many features; I'll talk about a few of them.

It has full MVC support, where I can choose to define my views declaratively, in different ways, or imperatively, in JavaScript - I choose XML almost every time because, ironically, it's the most clean and concise and like other declarative approaches, it prevents me from mixing up my controller logic with my views.

It has server-side and client-side model support with very accomplished data binding mechanisms, all the power and features I need to handle collections, objects and individual data properties in my apps.

Many of the clients I work for are international and multi-language support (including RTL) is a requirement that OpenUI5 satisifies with ease.

There's plenty more, but the bottom line for me, when it comes to libraries, toolkits and frameworks is the question: "Does it make me more productive?" With OpenUI5, the answer is a resounding "Yes".

I've had conversations with many people about libraries in general, and more recently with toolkits like this in particular, and there will always be personal preferences, strongly held opinions, and even biases that are hard to explain. For me, the bottom line with any abstraction is that question above.

FWIW, I gave a lightning talk on OpenUI5 at FOSDEM a couple of weekends ago: http://pipetree.com/qmacro/blog/2015/02/openui5-at-fosdem-20...