Multi-homed Internet sites become more and more widespread, due to the rising dispersal of inexpensive Internet access technologies combined with the growing deployment of resilience-critical applications. Concurrent Multipath Transfer (CMT) denotes the Transport Layer approach to utilise multiple network paths simultaneously, in order to improve application payload throughput. Currently, CMT is a quite hot topic in the IETF - in form of the Multipath TCP (MPTCP) and CMT-SCTP protocol extensions for TCP and SCTP. However, an important issue is still not fully solved: multipath congestion control. In order to support the IETF activities, we have set up a distributed Internet testbed for CMT evaluation. An important tool - which we have developed for multiprotocol Transport Layer performance analysis - is the Open Source NetPerfMeter tool-chain. It supports the parametrisation and processing of measurement runs as well as results collection, post-processing and plotting. However, its key feature is to support multiple Transport Layer protocols, which makes a quantitative comparison of different protocols - including state-of-the-art features like CMT - possible. In this paper, we first introduce NetPerfMeter and then show a proof-of-concept performance evaluation of CMT congestion controls which are currently discussed in the IETF standardisation process of CMT-SCTP.