I’ve been researching CBD e-liquids as well, when I was weaning off from pot and cigarettes a year ago. CBD had some benefits to me during that period, since the taste and smell are similar to the real thing, due to the added terpenes. Regarding the effects: it has less recreational value, during the onset you think you will get there, but will never reach to that point what you are used to with weed. It feels relaxed, chilled, a sensation of mellow wellbeing without the head rush. Like a weak xanax, but it might just be the placebo.
I was looking exclusively for liquids with 0%THC, made with CBD distillate since the target was to eliminate THC from my system. It has fit the purpose, simply for the flavor, the smell and habit. I used it with SMOK nano 1.5-ohm pods at 12W as it is thicker than regular e-liquids and needs low wattage not to burn.
Regarding strength: I went for 1000 mg/30ml=33,3mg/ml, better start mid-low and build up when needed and not to waste money.
My advice is to buy only from reputable sellers to be reassured of the contents. I went for the French manufacturer Marie Jeanne, I think they are also selling it in the UK.
Have fun and good experimenting, stay safe! This is mine: