These batteries are great for the price! They charge well in my Traxxas Duel ID Charger. In my Maxx they work great and I really like the extra hard case protection in case anything goes wrong. In my UDR I like to run just 3S because my UDR tends to break on 6S, so it was perfect for me but keep in mind only one of these batteries will fit in the UDR. On my TRX4 these batteries will work, but you have use a Velcro fastener instead of the original one on the TRX4.
Overall great batteries for the price! I would be happy to purchase these again.