I wouldn't call it "safe", and neither does the linked article: "Just make sure you realize that without a journal your filesystem is more susceptible to corruption and data loss if it is not cleanly unmounted (if the power goes out, for example)."
You won't experience data loss in normal use, but if the system ever goes down uncleanly (i.e., the battery runs out, disk buffers don't get flushed before a suspend to RAM that doesn't recover cleanly, &c.) between some data hitting a write buffer and that data being written out to disk, the lack of a journal will result in at least the inability to recover that data, and at worst a completely broken filesystem; it all depends on what's going on when (not if!) your luck runs out.
Considering the steadily decreasing cost of Flash and consequently of SSDs, disabling ext4 journaling strikes me as an extremely premature optimization; if you're going to do it anyway, and you have anything on the laptop you'd be upset to lose, at the very least make sure to keep good backups, because sooner or later you'll need them.
The article you mention states it clearly:
"Just make sure you realize that without a journal your filesystem is more susceptible to corruption and data loss if it is not cleanly unmounted (if the power goes out, for example)."
This does not mean that you will experience data loss. Only if something goes wrong and your partitions are not cleanly unmounted, the possibility of losing data is pretty high.
I would suggest that you did not disable journaling since your partitions contain important data.
