MySQL on SSD - what are the disadvantages?
Modern SSDs are a lot more reliable than people tend to think in these discussions if you buy decent drives. If drive failure is a concern then RAID the drives as you would with spinning metal based drives.

One concern with SSDs is write lifetime, but for all but pathological cases if you have good drives the reliability shouldn't be much (if any) worse than traditional drives. The other issue is random write performance which can be a problem on some drives under heavy write loads (this is mitigated somewhat with drives that have a larger "over allocation" factor, and you'll not find it slower than spinning metal manages). Neither of these issues is going to be significant unless you have write-heavy loads.

"20% of operations are inserts or updates" isn't particularly meaningful as they could be affecting one row each or many millions. From a performance PoV the best thing to do is test your app and run realistic benchmarks for it. From a reliability PoV with good drives you should be as safe as with spinning metal, though of course use RAID1 (or 10) and backups to cover all the bases as you would normally.

Any recommendation more specific than that is going to be very opinion rather than fact based. For my own PoV: these days I put SSDs anywhere where I can afford the larger $/Gb and cope with the smaller individual device sizes, but I don't trust a single SSD any more than a single spinning-metal drive so anything important gets both RAIDed and (more importantly) regularly backed up and those backups regularly tested (a step that too often gets skipped).