A balance, as long as the knife edge is kept in good condition is kept calibrated by the fact the physics of a balancing masses doesn't change or drift over time. You often do have to clean the knife edges periodically. Keeping an inverted Baggie or other dust cover over the scale pays big dividends in lowering maintenance.
Either capacitive or strain gauge load cells can and do drift off zero and lose accuracy over time, and some are just better designed and made than others. I have heard of folks getting the $30 scales and having them work great and others having them work very poorly and ultimately returning them. My copy of the PACT scale that's worked so well for Matt drifts badly, and when I got a lab grade scale with ten times higher resolution, I found one of its check weights was off by almost a full 0.1 grains, which wasn't helping the calibration. I wound up having to keep mine on a small granite surface plate to keep its temperature even and to put a grounded Faraday shield around it and to run it off an isolation transformer with grounded shield to get it to settle down. So, despite its price, it's another scale for which it seems that either you get a good one or you don't.
I also paid over $100 for a CED pocket scale a few years ago to have something truly portable and with a wind screen for my range box. It works perfectly. Very stable. Never loses calibration. Then I noticed one day the guy I bought it from (RSI) had stopped carrying them. I called and asked why? Same problem. If you got a good one, they were great, but if you didn't, they weren't, and he got tired of dealing with returns and returning his returns to the factory. I got lucky that time, it seems.
So, whatever you get, be prepared to hold the maker's feet to the fire until you have a good copy in your hands. Digitals are faster settling and easier to read. Some, like the PACT, interface with dispensers that make dispensing weighed charges very fast, but you do have to have one that holds its zero for that to work well.
Probably the best deal on a digital scale today is the one Brian Enos sells for $75 on his web site. It has the only 20 year warranty I've ever seen on an electronic scale. They must have a lot of confidence in whatever they are using for a load cell? In any case, it gives you plenty of time to discover problems and get it replaced if need be? There is a less expensive version available with half the weight capacity in the same housing from different suppliers, but I would not go for that one. The lower capacity suggests it has a different load cell (transducer).
Home made check weights don't give you absolute calibration, but after calibrated check weights have got the scale's absolute accuracy reasonably close, trimming a coil of stainless wire to match a particular load is something that offers a real convenience at times. It lets you make a quick check for drift without putting a heavier check weight on the scale that could lose the zero in load cell hysteresis until several regular charges have been weighed.