If you decide to try one out I had posted a quick DYI on how to make your own SIP below 
The 7.5 gal are pretty easy but it all depends on how big you grow your plants and how long you may be away from your plants.
The 7.5 has a 2 gallon reservoir.
The 12 gallon and larger size totes really allow you to have larger reservoirs if you choose to.
Here a pic of shoreline just before she went into flower so you can judge plant size.
If you have any questions if you decide to build one please feel free to hit me up or you can also post in CrunchBerries’Probiotic SIP Thread and I am sure you will get all kinds of assistance…
I would also like to say that **this information comes with a warning.
Once you grow from a well constructed /set up SIP you may be forced to switch much of your grow to SIP’s 