@Saqib_Ansari We have reached this stage UI as of now. This has been designed based on real world users response/feedback to existing ERPNext POS, their actual needs and to ensure all the functions are available bang in front. Over past two years we have pushed ERPNext to all our customers and have improved functions wherever possible. We have seen many POS ourselves right from MS Dynamics, Wincor Nixdorf to the unknown ones. We have also sold and installed few other POS which are easy to use than ours.
This is being built on V11 and is targeted to finish by next week, hopefully.
There has been slight modification of the POS codes and since then users have not complained about any missing invoice. In fact some to the forum users have also found it to be stable.
From your post my understanding is that all POS invoices will be in the local browser cache. Please clarify this further. Frankly, I would not go down the road of end of day sales positing until and there is a tried and tested database on local machine, something like MS SQL Express, to store the data. Its too much of risk already with offline POS even though it syncs at 3 minutes interval. Business owners want real time reports which is not possible in end of day process.
To be realistic you will need to refactor the whole POS to make impression to end users especially the retail supermarkets etc.