I think you can trust Agilent's statement regarding their specs. You'd have to define the meaning of 'tough' to know it meets the specs.
I don't own the 1253 but do have a 1252a. They are very similar. It does not have a specific IP code rating but the spec sheets say :
Operating temperature Full accuracy from –20 °C to 55 °C
Operating humidity Full accuracy up to 80% R.H. (relative
humidity) for temperature up to 35 °C,
decreasing linearly to 50% R.H. at 55 °C
Storage temperature –40 °C to 70 °C (with battery removed)
Altitude Up to 2000 m
Pollution degree Pollution Degree 2
and shock/vibration Tested to IEC/EN 60068- 2.
To test it, I put the 1252a in a refrigerator and freezer, then in a summer sunlit patio to 80+F RH 80% then tested the accuracy. 1252a meets them all well. Taking the meter out of a cold environment causes a lot of condensation, enough for droplets of water to fall off the input jack.
Now, there is no specific mention of drop test, and shock/vibration can be equivalent to a drop test but its not clearly defined. I haven't dropped mine yet, fortunately.
http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F7770%2F21355%2F00990367.pdf%3Farnumber%3D990367&authDecision=-203Its a good meter, made to take use in a lab and maybe spills from a bench to the floor, some field work, but its not a built like the Fluke 87V [ which has only IP 30?? IIRC] but has been proven in the field, or the 1272a, which is rated 54.
In my use tough means drop from 3' to a concrete floor, exposure to fulll sunlight, 100% RH to 100F ambient temp, and sea spray, as its used on boats. No specific exposure to sand and mud to foul the input jacks, but they have been, and cleaned with compressed air. So far the 1272a and the Fluke 87V do well.