I solo playtested using my GW orks and the Blood Angels as Forgefathers. The game still needs some fixes, but hey it is first edition and free. They are going to release 2nd edition this year and Ronnie mentioned "tanks" (I hope so) . Im sorry, I dont remember exactly what rules I had the problem the most, but Alessio and the whole team is working on them.
Some things I like about Mantic:
-Price/quantity (the more you buy, better for you)
-Simple and short rules
-Some minis like the space rats and space dwarves are not in GW
-GW compatible with most minis and the other way around.
-The rules and army lists are updated every year.
Some things I dont like about Mantic:
-Lack of vehicles
-A few molds are not good
Overall I have Warpath and Kings of War rules and army lists printed in english and spanish, but I have not been able to get no one to play it. Everyone is brainwashed by GW. If you have a group go for it!, but I recommend more Kings of War because rules are more polished.