I have one and the easiest way to clean it is to use Tilex. It's a shower cleaner spray designed for cleaning tile and scum. There is a lot of bleach in it and it sprays out nicely. As Darwin said a little extra effort will get it clean. The Tilex spray is nice because it gets in the little cracks/step. Spray and let it sit for about 5 mins the rinse hot and use a scrub pad. BOOM, clean.
I personally prefer a realistic looking enclosure and find it worth the effort. However I completely understand that people who have a lot of snakes need to be efficient and IF you are THAT person, by all means go simple.
But, if you like to enjoy your snake in a semi realistic/natural environment, change the water often and just spray the bowl with Tilex and use a buff pad to clean it.
I just get too much pleasure out of this and will take the extra effort to clean it.
Again, not knock on the simple, efficient setups as it's purely a personal choice.
Try the Tilex and just change the water more. If you go on vacation add a second water bowl and maybe have that one be simple. We came back from an 8 day trip and the water got scummy it's just the way it is unless you have a friend/relative change it.
Good luck.