A grid is usually a better option than a memo, because the painting of the cells is usually more optimized by better use of clipping. E.g. when bid or ask has changed only the cell for bid or ask will get updated. When trades change, only trades will updated. And that is much, much faster than a full repaint of a memo.
But what molly says is true: depending on exchange, updates are such that they can't be followed by the human eye: they are indicative only. Most trades are therefor effectively done by trading algorithms.
Human trades are done by setting a buy or sell moment (aka stop-loss) and executed automatically when the actual price hits the spot. If you don't trade like that you are always behind the market.
A professional - like my old employer Alex/Binckbank - team can reach
visual updates of 15 Ms in custom software and 25-30 in a browser and that is too slow
to follow the markets. Although every and all actual trades could be registered in the huge Oracle clusters (buffered). Depending on data provider, but that's a different story: we've see data providers drop trades, which is unacceptable.
Note pricing is not that important: use a priority queue to display actual trades first, volume second and bid ask last.