I originally bought these I think back in 2012 or so and at the time, I felt they were great. Flat, neutral sounding with great isolation.
My usage of the SE215 could be described as "every day". I am not a professional musican using them on stage or anything, but I did use them for focused work, and enjoying music intensely. The SE215 are great in this regard as they do not leak sound, aiding in quiet environments and being respectful of others.
I had to send my first pair back to Thomann for repairs I think in about 2014 as the cable had become faulty, but this was without a hitch and gives me confidence to buy in the future.
Looking back, now in late 2019, there are far better and cheaper alternatives on the market. I would say the SE215 sound very closed and muffled when comparing to even my bluetooth silicon tipped Galaxy Buds. For comparison, I used KZ ZS10 pro IEMs, which are half the cost, the closest I have in price in this form-factor.
Granted, the SE215s come with a great cable that is long enough to be suitable for over the ear wear, with a stiffened portion near the ear to aid in looping around and keeping in place. Something of this quality is very rare with Chi-fi. Also, with the SE215 you get memory foam tips and good soft carry case - things that with Chi-Fi you'll have to purchase separately.
At the reduced price that the SE215 are often available now, they are probably a good deal - trusted brand, not coming from some unknown shop/factory.