I have two Vapeonly BCC Mega's. I can't say enough good things about them. I've been waiting for a product like this for years. I've tried a lot of attys/cartos/clearos/tanks and I've never been completely happy with any of them. The Vapeonly is the first product I'm 100% happy with. I wouldn't change a thing. A lot of thought was put into the design and it shows. They raise the bar to another level IMHO.
They do not leak no matter what. I carry them around in my pocket all day without worrying about leaks. I'm talking loose, not screwed into a device and without a drip tip installed. I have yet to have a dry hit and I never worry about the tilt or angle of the device. They're silent! No pops. No gurgles. No whistling. With the drip tip removed, you can sit them down (upside down) and not worry about them falling over or rolling away. They're easy to fill and easy to clean between juice changes. I'm also loving the ability to use my own drip tips and/or go commando (without a drip tip!) They look great, very "acceptable" for public use.
The coil heads are marked with the resistance value on the side. The heads are easy to push in and hold tight. The heads can't come loose because they're push-in rather than screw-in. I haven't had the need to rewick yet but I've torn down a spare head and it looks like rewicking will be very easy.
I use the 2.4ohm heads at 3 to 5 volts. Most of my juice is 80/20 but I've tried 50/50 and 100% pg with good results. I tend to prefer bottom coil designs in general for what it's worth.
Regarding tight draws, the bottom part of the 510 connector is completely sealed. The air inlets are two holes above the connector threads. The sealed connector design is awesome for preventing leaks. However, the air holes can cause a tight draw if you screw the Vapeonly too tightly into your device. If you can't loosen up on the screw-in, you can line the air holes up with the top notches that are in most 510 connectors. Another solution is to buy a 510 "shorty" extension and dremel a little off the top so you can screw the Vapeonly hard into the extension without covering up the air holes. I've done that with other devices that had the "above the thread air holes" but I haven't felt the need to do it with the Vapeonly.