Sphider comes in two editions, the legacy version and a PDO version. The legacy version is definitely the more stable, faster, easier to maintain version. The PDO version exists primarily for those who are restricted by their shared hosting providers.
Shared hosting has its advantages in that it is very cost effective (cheap) and very simple to use. It is great for personal use or for small businesses or organizations just getting started on the web.
But shared hosting has its downsides, too. It isn’t nearly as efficient, isn’t as secure, suffers from limited resources, and has limited functionality. One of the features commonly lacking in shared hosting is MySQLnd. Thus the need for PDO.
The are quite a few users of the PDO edition, and to simply drop PDO would be a great disservice. On the other hand, trying to keep the PDO edition in sync with the legacy edition is getting harder and requiring much time and effort.
The PDO version, as it stands, is quite usable. It is PHP 7.3 compliant, so it should be reasonably set for awhile, as the majority of shared hosting plans are still at least a few versions behind 7.3!
The thought is that the time for legacy and PDO to part paths, with most future effort going into the legacy edition. Because of the user base, PDO version 2.4.0 would remain and receive hot fixes as needed.
No decision has been made and feedback will be given consideration.