If you assume a constant failure rate and continuous usage, you can convert MTBF to average annual failure rate (AFR) with this formula:
AFR = 1 - e^( -8760 hours / MTBF in hours )
So, for example, MTBF of one million hours corresponds to an average annual failure rate of 0.87% , meaning that if you had one thousand devices running for a year, you would average 8.7 failures in that year (assuming you immediately repaired or replaced any failures to keep the total operational count at 1000).
However, this type of analysis is so simplistic as to be almost useless for typical consumers to compare SSDs (or HDDs). One reason is that the actual failure rate probably follows a bathtub curve, with higher failure rates at the beginning of life, and higher again at end of life. So this analysis is only valid during the middle of life. But many consumers are probably interested in failures during the beginning of life period, not just the flat part of the bathtub curve.
Worse is that MTBF numbers are determined using a highly controlled environment. For example, a number of SSDs may be exposed to a certain workload, connected to certain hardware, at a certain temperature, and then run until a specified number of hours (or failures) have occurred, and that data is then used to compute MTBF. But this obviously does not include failures that may be the result of different workloads or use with different hardware.
Even worse is that different manufacturers use different techniques to determine MTBF, and the details are rarely specified.
So comparing MTBF numbers given by SSD manufacturers is not likely to yield any useful information.