You don't need to calibrate most of these meters. I've been using one for 6 months and it's still spot on with no calibration.
At this rate I would be satisfied if I burned through one every few months, however the ones I have keep on tickin.
It's up to you, these are so easy to use it's ridiculous, you just turn it on, dip it in the water, and it shows you within a millisecond what the TDS of your water is. Those strips are so inaccurate that they only show to the nearest 50, 70, 50, 80, 175 AND you have to use your eyeballs to judge which shade of BROWN it is... how ridiculous is that. With these, you can test every day 5 times a day for 6 months and it tells you in exact parts per million what your TDS is.
At the very least, get an API liquid GH and KH test kit. They're more useful than a TDS meter, but expire faster and are more difficult to use, but they tell you your GH and KH.
I use mine in conjunction with my TDS meter to figure out how much extra "junk" is in my water. IE. if my GH is 5 and my kh is 0, i know i have roughly 90 ppm of hardness, the rest of the ppm is nitrates, other minerals (such as aluminum, selenium, zinc, etc since I have a mineral stone), and other biproducts from plants and animals. So I know that with my mineral rocks and my GH of 5, my "clean" water is a TDS of 180, when it gets to 200, I know I have enough nitrates and other gunk in the water that I need a water change, which will lower it back down to 180 TDS.
It's not a massive advantage for the hobby shrimpkeeper, but it lets me know at a glance how clean my water is and roughly how hard my water is.
Also, if you're using ANY tap water in your tank, it'll tell you exactly how clean your tap water is (which for most folks is downright disgusting 350 ppm of TDS is average).