All in all I am really impressed with the otolens’… I must admit - I have been something of an “open fit” bte fan over the past few years and have probably even been a bit blinkered - However, trying not to be too biased I have recently been trying out the Starkeys (first series 11 cics and now otolens’)…
Firstly - it is absolutely amazing how they make them that small - remembering that the battery takes up half the room inside!
As far as comparisons are concerned, I’m mindful that I am a sample of 1 so you won’t see any of my opinions (and they are only opinions) in any scientific journal 
There are pros and cons with all hearing aids. The pros of the otolens’ are that they are invisible, they are reasonably comfortable (not as comfortable as an open fit bte though in my opinion - although I must admit not having anything behind my ear is nice), no wind noise, have no feedback, great for normal phone use… and sound pretty good…
As for the sound there are a few issues… firstly - they don’t have directional microphones - so while I can hear fairly well in noise, I can hear better with my BTEs… Also the nature of custom hearing aids mean that they don’t amplify as high along the frequency spectrum as other hearing aids.
Also, depending on your own priorities you might like wireless/bluetooth compatability… the otolens doesn’t have this (and if they did would have to be made a lot bigger - hence defeating the purpose of what they were designed for). They also don’t have some features that are available in other hearing aids.
The only other thing about the otolens’ is that because of where they sit in the canal it is virtually impossible to adequately verify the fitting (i.e do real ear measurements or ‘speech mapping’) - so as a clinician you need to really rely on the client giving you honest feedback (which is hard! ever been asked “how does that sound?” - my response to that question in a clinic office would be “buggered if I know - it just sounds different!”
Having said that - if you’re after an invisible hearing aid, are brave enough to get a deep impression taken, are willing to be patient and communicate issues with your audiologist, and be aware that they mightn’t be right first go - then I’d highly recommend at least trying the otolens… I’ve had some clients who have loved them, some who didn’t want to pay the price for them, some who found them uncomfortable, and some who (like me) initially found them uncomfortable, but after a remake are very happy.