Try to buy all the same trimmers, blowers, etc. That way you only need to keep one set of filters, plugs and fuel filters when the time comes. Also, you never have to try to remember any model #'s, they're all the same. Also, if you're a big outfit, try buying all the exact same model mowers. It makes repairs and parts replacements easier for the mechanic. Also, he only has to "learn" one machine, that way he can work faster without having to remember the nuances of 7 different mowers.