Similar in some ways, yet quite different, could go into more detail in a comparison thread probably, but speaking with a focus on the BAK, there is more open-ended power and versatility although the bowl is quite a bit smaller and the heating is much more pure conduction... The quick session style, like using on demand mode in the solo, can be similar in a sense, however S3 did not seem to do anywhere near as well with a whole nug for me... Furthermore BAK is only available in the x configuration with a mod, you could get it all together set up however, it is still not really as sleek as solo although it could be quite a bit smaller of course with a single battery mod... Finally, I do really enjoy the BAK vapor quality as one of my best ever in all categories for flavor with such a simple build and pure materials/pathways, and of course the power and extraction style done this way just really slap and smack, even if it is not really one of my smoother hitting vapes, not sure I would count solo as one either, I do prefer to use both at lower temps personally however and they are both wonderful dry and impressive through water