What are Filament Style LEDs and how do they work?
This is not a new technology, but simply a new manufacturing process.  They are "normal" LED's but each "filament" is a "long and skinny" arrangement of several small LED's in series.  Each individual LED within the filament puts out much less light than a typical larger LED, but they add together to make more light.

It is a nifty new way to package LED's.  Can look really nice when used well.  The individual filaments are available on eBay nowadays, and several bulb manufacturers have started working on making "bulbs" that use these filaments in various ways.

There are some negatives to be aware of.  Since each filament is a series array of many small LED's, the filament will die completely once any one of the many LED's in the filament goes bad.  So an expected failure mode with these would be to see a bulb that has several filaments, and one or more of them would be "burned out".  No doubt manufacturing advances over time will make this less prevalent.

"Are these any good?"  They have some benefits and drawbacks.  Biggest drawback is that they are new, and have not undergone the same set of engineering improvements that other LED bulbs have now gone through.  I would describe them more as "promising" and "interesting" rather than "good".