Oh alright, is there an open ear headphone of equal quality?
When you say of "equal Quality" that is really subjective. Pretty much every headphone is a little different.
Closed will generally always have better bass extension. The Sennheiser Momentums outperform even the HD 650/800 when it comes to low-end performance.
Unless you are talking about Open or closed (Doesn't matter) Planar Magnetic Headphones... those will have the best Bass performance period... especially the Audeze LCD 2/3 and Stax SR-009 (Both Open, Both incredible Bass Extension). This is generally due to the flat, thin, large diaphram used as a driver... which provides several times more surface area to produce sound than conventional Dynamic Driver headphones.
The advantages of an open-back design are a much more open, and natural sound-stage... They will sound much less congested than "closed" headphones.
The highs will sound much more sparkly and airy without actually becoming brighter in their sound signature. Voices will sound more realistic. It all has to do with the acoustics of the headphones.
So as far as "equal quality".....
At the same price point, I cannot think of a single "open" headphone, personally, that would have the same kind of low-end performance as the M-100 or Momentum. But there are plenty of good options if you are willing to sacrifice the low-end performance for an improvements in other areas of sound.
For instance, you can get the Sennheiser HD 650s, which still have a nice low-end (Not as good as the Momentum), and will generally destroy both of those headphones in every other regard. They can be had for about $350 fairly easily.
They will also require a decent amp too.