LIKE APPLES AND ORANGES
The Tesoro is lighter. The Garrett, while well balanced, is clunkier by a long shot. And don't even think about hip mounting the 1350's battery pack. That is a fiddly affair and you risk damaging the power cord.
The Tesoro has one really cool feature: the sum mode. It's what some might call a confidence mode. The more you gather information about a target as you swing, the more confident the detector will become in its ID of that target. The Garrett has nothing like that. On the other side, the Garrett is very accurate - when it locks on, you can be very sure that it sees the target as it calls it.
The Garrett has 'Graphic Target Profiling' to give an indication of a targets size. I find it helpful - others find it annoying.
The Cortez has a display that is peckish to some, being hard to see. The Garrett is wide open and very easy to see. The Cortez offers a bar graph and VDI information model, the Garrett uses a 24 segment ID line with pointer and cursor.
Cortez: Analog control model, with knob interface. The Garrett is completely digital, with tactile control pads.
Cortez: It has a true all metal mode - the Garrett doesn't. I has a 'zero discriminate' mode. This is its only fault as far as I'm concerned.
Cortez uses a preset GB in DISC, the Garrett is auto-tuned to ground conditions, all the time.
There have been some issues with the Cortez's battery compartment doors popping open. The Garrett has some issues with the battery cartridges being weak. Both concerns have been rectified and will be addressed by the makers for free, should they be a problem with YOUR unit.
The Tesoro is smooth and silky in its response audio, although it only offers a single tone. It is amplitude modulated for depth indications. The Garrett is digital, with an on off type response. It gives a shorter response on deeper targets. It offers three tones, the highest being the Garrett 'Belltone' - "The Sound Of Money!" Some people find it annoying.
For pure depth performance, I'd give the edge to the Garrett.
Overall, they are not even good comparison material. I'd suggest you allow them to each stand alone, on their own merit.