The MacBook no longer had a functioning hard drive, so we are unable to give before and after test results, but it flies along with the MX300, starting up in just six seconds. And the dreaded beachball is noticeable by its absence, though admittedly the 16GB of RAM in this particular computer probably helps with that.
Crucial claims sequential read speeds of 530MBps and 510MBps writes. BlackMagic's Disk Speed Test program reported 473.5 and 411.7MBps respectively. That's not to criticise the drive, rather to show that even relatively old computers can benefit from the performance. (If you're running a recent version of OS X on an older Mac, installing an SSD will almost always give it a new lease of life.)
The 750GB version sells for about $300, which roughly means you're getting 50% more storage for the same money as some other brands. Sure, for hard-core techies there's more to the equation than just price and capacity, but the MX300 seems to hit a sweet spot with regard to those two factors. A 500GB drive seems a bit too squeezy to us, especially in a notebook where an external drive is an inconvenience, while a 1TB SSD is a bit too expensive.
Also disappointing is the lack of clarity about the use of TRIM. Recent versions of OS X have allowed users to enable TRIM on third-party SSDs, but there have been reports that the firmware in some drives — including certain Crucial models — have bugs that can lead to data loss in certain situations if TRIM is enabled.
We asked for Crucial's recommendation about enabling TRIM on OS X El Capitan via the "sudo trimforce enable" command with the MX300, and the response was: "Our drives feature built in garbage collection, and thus in most cases TRIM is not required. Apple notes risk and limits liability when users enable this command. We would suggest a user read and understand this risks and their potential impact when considering use of this feature."
Crucial also says that active garbage collection requires the drive to be powered up and left idle for six to eight hours – unless you make a deliberate choice, that doesn't happen very often with a notebook. The general consensus seems to be that whatever garbage collection mechanism is built into a drive, TRIM helps and can't do any harm (assuming it's properly implemented by the drive), but we intend to hold off enabling TRIM until we hear reports from other owners.