DEX is FW developers. It integrates with Target Manager and allows debugging of applications from PC.
rif is mandatory for all PSN games or DLC, except for the ones signed as demo or as debug (fself).
4.88 is more stable than 4.89, even on OFW. Evilnat 4.89.2 BETA seems to be as stable as 4.88.2. So both are fine.
Evilnat 4.89.2 BETA is recommended if you go online.
Rebug Toolbox 02.03.06 was modified to work on Evilnat. But Rebug features will not work anyway.
The features that work (and new ones) are already available on Evilnat CFW under Network > Custom Firmware Tools menu.
Rebug is superior because it allows debugging in DEX mode and has some debug features not available on Evilnat. It also supports OtherOS+.
Evilnat has the advantage that it allows PSN access on
NP environment. It has Cobra 8.3 and an extended xai_plugin to support the new features in CFW Tools menu. Also has a failsafe LV2 kernel that disables Cobra automatically if it fails to load.
IMO, Rebug 4.84.2 REX modded with Cobra 8.3 and xai_plugin+CFW Tools is the best option of all.
Although I'm currently on Evilnat 4.88.2 Mamba 8.4.