Simply speaking, the original udp2raw has more features, udp2raw_mp supports more platforms.

Differences in detail

You need to install pcap first before using udp2raw_mp. No similiar requirments for orginal udp2raw.

There is no option -a (automatically add iptables) in udp2raw_mp, also there is no --clear --keep-rule in udp2raw_mp.(but -g option is still there, so you can add iptables/firewall rules manually). In other words, in udp2raw_mp, it's users' responsibility to manage iptables/firewall rules.

There is a new raw-mode named easy-faketcp mode in udp2raw_mp. It is able to handshake with a server of faketcp mode, without the help of firewall rules, though the performance is not optimal.

There is no linux-specified options such as --lower-level and --force-sock-buf.

Other problems which may be solved in furture

udp2raw_mp will exit after recovered from hibernation. Use the trick in this link as a workaround.

Connection of udp2raw_mp wont persist after network changing(For example,you switched to another wifi) as orignal udp2raw.

There is no --fifo in udp2raw_mp.

The random source of windows version of udp2raw_mp is currently pesudo random, which may affect the strength of encryption.