I've owned 3 Topping units thus far, two secondhand, no failures yet.
The one time I bricked one by updating it with the wrong firmware, their service department got me straightened out in under 24h.
That said, threads like this are not a good way to assess reliability.
What you want to know is the overall failure rate compared to other brands. What you will get is exclusively complaints about failures, fanboys excusing failures, or people with nothing better to do commenting (me). You won't get actual data, and whatever you do get is definitely biased and impossible to compare to a baseline.
The data you want is exclusively in the hands of Topping itself or possibly some retailers who deal with returns. Unfortunately, they aren't sharing this data.
As such, the more important thing to consider is how well their service department handles failures, if one occurs, and how long the warranty is. Personally I'm not sure about this, but it's easier to find out.
If you really want to know about failure rate, I would suggest going through Amazon reviews of several DAC brands and searching the reviews for keywords associated with failure, like "broke", "bricked" "died", etc. Compare the percentage of reviews that mention those keywords and you might be able to form a rough, relative estimate of reliability.