I've used both Rodent Pro and American Rodent Supply. Very similar in price with shipping... but I was MUCH more impressed with how clean and neatly packed the feedrs from American Rodent Supply were. My feeders from RodentPro seem to always have a lot of urine/bedding mixed in and the rats are just piled into a bag. ARS feeders are lined up neatly in heavier bags and are usually very clean.
Just my experience. Most large breeders do have size guidelines and photos on their websites.
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Lauren Madar
www.ophidiagems.com
1.1 Hog Island Boas
1.1 Hypo BCI
0.1 Sorong-type GTP
1.0 Normal Ball Python
1.1 Surinam BCC