There are a lot of options for bowden couplers and while I haven’t tried them all, here are the ones I’ve tried and my experiences with them. They were all used with 1.75mm filament, 4mm teflon tubes, a BondTech extruder, and an E3D v6.
My first prints with the Tiko was terrible (not unusual for a 3D printer), I used the default settings including the default temperature of 210°C and it was clearly too hot, making the test print come out a melted mess. No problem, I know how to fix that. So next I tried 190°C and it came out very underextruded. The clicking sounds made it clear that the something in the extruder system wasn’t keeping up.
Along with some 16 thousand other people, I joined the Tiko Kickstarter in the spring of 2015, and it recently arrived in the last days of 2016. The Tiko is an interesting printer, a mini delta, costs less than $200, includes built in WiFi, is fully enclosed, is fanless, comes with a built in slicer, is compatible with other slicers and filaments, and is easy to setup. And although it doesn’t come with a heated bed, it’s also compatible with the heated bed of my Eustathios (pictured above). As of early 2017, here’s a few of my first impressions (I expect things will be changing quickly).
I’ve had some issues with warping when printing with eSun PETG, which was surprising since I’ve never noticed any warping with PET before that. Since many people seem to be getting warp free prints with eSun PETG, I assumed it might be caused by PETG from the early production runs. So I purchased a new spool, and it does look quite a bit different (rougher texture to the filament). For a test object, I used a fin on my ski pulk as that was one of the prints I was having troubles with. The original was printed as a vase print, with a 1.5mm extrusion width. The retest was done at a 1/3rd scale, also as a vase print.
For all the people who have asked about filaments, here's my list, spread across 8 different posts. This list includes over a hundred filaments, with pictures, measurements, and impressions. All are 1.75mm. Please don't read too much into my opinions, there's a lot of variation in filament and printers, and my opinions apply only to the spools I have on hand. I try to be objective with these opinions, but my preferences and biases affect my opinion, so keep that in mind when browsing this list. Also be aware of the date, some of these filaments may no longer be available, or may be different from what is currently available. I sometimes describe how I use and print some filaments just to provide another data point, it's likely that your optimal setup will be different from mine.