VWIC-2MFT-E1 only can be used as structured, i.e. you have only 31 channels available, so maximum 31 x 64kb = 1984 kb.
If less than 31 channels are used, the term "fractional E1" is also used, and "channelized E1" if one or more links are combined (e.g. 2 links of 8x64kb=512kb) on the same interface.
VWIC-2MFT-G703 can also be used in unstructured (g.703) mode so you have 32 x 64kb = 2048 kbps available for use.
Which one you need is dependent on your application, and on what your telco can offer you (and at what price).
hth
Herbert
