GSL Isolators

Has anyone had any experience with the GSL EB!-100HD 100/150 AMP Electronic Battery Isolator( $150). I have bought an 40ltr Engel and intend to set up a Deepcycle battery in the rear of vehicle(Pajero) to run it on.Battery set up will be removabale.I have read every forum on this subject and am still confused. The GSL has been recommended to me and the Federal deep cycle auxillary battery( $240) will be independent of the main battery and charged by the alternator via the GSL device which is automatic and charges the auxillary battery when the main is fully charged.The service centre assures me there is no possibility of main battery being run flat,no surges to fry computers or wiring. An Anderson blade plug will be used ($40) and 15amp cable to reduce loss of voltage.Initially armed with no knowledge (still extremely limited) they were all over me like a rash to set up the system. Called today armed with the forums possible problems and recommendations they were not overly cooperative to spend the time discussing the set up unless I booked the job in. Will the above serve it's purpose to run the fridge for two to three days at a time untill 240V charger is used?. Do prices seem reasonable? I know it is a repetitive boring subject but maybe some one can help on the above.