I switched from Microsoft Office 2010 to SoftMaker Office Pro 12 but recently switched back due to a few notable bugs and excluded features that turned out to be too much to accept.
One biggie is that in PlanMaker - similar to Excel - it insisted on saying I was using the German version - but only with regard to the date format. I would have to change it every time I entered dates in any spreadsheet. Support insisted that it should be using the Windows Regional settings on my computer, but that is US English and PlanMaker agreed - except for the damn date format! Also, PlanMaker always puts date columns in "latest date first" or descending order, which is the opposite of Excel. Besides that, while PlanMaker does use functions like Excel, it doesn’t recognize formulae already created in Excel when you import Excel spreadsheets, thus all my existing formulae were considered invalid and I would have to recreate them in a manner that PlanMaker understood - which was not always easy to do.
Bottom line, I wouldn’t always remember to fix all PlanMaker's little bugs before sending the spreadsheet out and recipients inevitably got confused! I reinstalled Excel last week.