I have kept at least a dozen different L-numbers in my planted aquariums without any incidents, and I believe that there is a lot of misleading information concerning their behavior.
Many of the places where the more common L-numbers are caught are rather without vegetation, and a great deal more plecos than previously thought demonstrate a tendency toward carnivorous feeding habits. I doubt plants are a significant element in most of their diets, and the dentitions of many of them support this. Without a doubt there are herbivorous Loricariids, but I don't think they're all that common. The standard LFS-available plecos seem to prefer meaty foods and algae (wafers) above plant matter. Well, at least IME.
I personally have had more problems with snails than any pleco. I think the main issue that you need to watch out for is their impatient romping around on the substrate, uprooting plants that you are trying to get to take. I'm still having trouble with my Ranalisma because they continue to knock it around.
A clown pleco should be fine, but it all depends on which one you get. I can think of a dozen different L-numbers I've seen listed as "Clown Pleco", and there are oodles of species in the family with similar/identical markings.
Mine come out when the food goes in, and after dark they like to scrape the algae off of the filter lift tube and the overflow ramp. It's kind of cool when they do that, I can hear their teeth scratching on the plastic.