There are hundreds of office chairs out there in the market, all purporting to be ergonomically designed but you really do have to be very careful about what you are buying.
There is no recognised definition of what an ergonomic chair is, so it really is “buyer beware” with these chairs
Ergonomics means “the applied science of equipment design” which is suitably vague to cover most things.
A cheap chair imported from China could be said to be an ergonomic chair because it goes up and down and the backrest is adjustable, and it is shaped to follow  the contours of an average back, but compare this chair to a quality ergonomic chair from Pledge Office Chairs for example and the difference is obvious.
The quality ergonomic chair will have been a result of many years of research into how we use a chair in the office, what we expect from it, and how it can be best designed, using  the latest technology, to give us the maximum amount of support for the longest amount of time, for a price which  represents good value for money.

Much of the quality of a truly ergonomic chair cannot really be appreciated just by looking at it, or even sitting in it for a few hours.  Most chairs will feel comfortable for a short while, especially if your old chair was ready for the scrapheap.

A cheap operating mechanism will feel just the same as a top quality one, at least initially.  However a few weeks or months later, when the quality office chair mechanism still feels and works like the day you bought it, the cheap one is beginning to show why it is cheap.
Inferior materials and construction means bits wear quickly and bearings start to feel rough.  The chair may be guaranteed but as it hasn’t actually failed then nothing will be done about it.

So you will have to live with this inferior chair, wishing that perhaps you should have sought some advice from an office furniture dealer before buying a cheap ergonomic chair.  They want you as a long term customer, which means keeping you happy, and will therefore be keen to sell you what you should be buying, because it is the right product, rather than what you want because it is cheap.

Whilst it is true that a good quality office chair will cost you a significant amount of money, it will last longer, give you less trouble, take more weight, be more comfortable, and have more levels of adjustments than a cheap basic chair.

In the long run it will prove to be much better value for money, which makes good business sense, and it will be less likely to permanently damage your back, which as they say, is priceless