Replace old XP400 with new Autel XP400 Pro?

Answer from an Autel user: the difference between the two is that the pro version supports much more processor, so unless you read processors, no reason to change, and of course we can put it on any autel im508 and 608

Answer from an Autel chief engineer: The used xp400 is not bound with im608 (they are independent), you can buy xp400 pro instead, and then sell xp400. It can be used perfectly with other im608 device. 
You can sell yours on eBay for close to cost paid. Help offset the pro cost. But many people choose not to sell it. To be honest, it’s good to keep it as a backup, in case some problems occur and the pro is stop working. If the pro will not work anymore for any reason, you can still finish the job and charge the customer.

Comparison: Autel XP400 vs. Autel XP400 Pro vs. Xhorse VVDI-PROG

Features	AUTEL XP400	AUTEL XP400 PRO	VVDI PROG
EEPROM read/ write	330 chip types	445 different chip types newly added support (AM29FXXX seriesMB29FXXX series）	429 different chip types
MCU read/ write	1541 chip types	2067 chip types	1758 different chip types
Engine ECU read/ write	40 chip types	41 chip types add write support for SIMTEC76(AM29F800BB)_WRITE	Engin ECU read (74 types)
Immobilizer ECU read/ write	168 chip types	181 chip types	171 chip types
Odometer read/ write	read odometer module 9 types	read odometer module 171 types (update in July)	read odometer module 171 types
Airbag read/ write	read airbag module 5 types	read airbag module 5 types	read airbag module 54 types
Frequency detection	315/ 433/ 868MHz	315/ 433/ 868MHz	N/A
Key read/ write	support	support	N/A
Unlock key	N/A	support 11 key types (Audi/ BMW)	6 key types
Write key via dump	For Mitsubishi, Suzuki, Fiat, LandRover, Jaguar	For Mitsubishi, Suzuki, Fiat, landrover, Jaguar	Support for 40+ vehicle makes
Easy to use/ stability	1. menus are too valuable and can’t select intuitively 2. with high-definition wiring diagrams (not sufficiently covered)	1. stability of key read/ write, chip read/ write, IR key read/ write are greatly enhanced. 2. menus are too vague and can’t select intuitively 3. with high-definition wiring diagrams (not sufficiently covered)	1. menus are clear and easy to use 2. with high-definition wiring diagrams (sufficiently covered) 3. high stability of chip read/ write

Source: https://lauranotes.com/autel-xp400-pro-vs-xp400-vs-vvdi-prog/ (click to get more info about xp400 pro)

That is, Xp400 PRO IR function is more reliable, and it has more chip reading capabilities.