Honestly, I don't really use it now as it is because it's still more efficient to 'manually' make requests in a few different Search Engines or websites using their own specific way of working, but I look forward very much to the future improvements of what could be a very useful and powerful addon!
- the main drawback I think at this time is that their is too few SE choices and more important, we can't add any of our choice? (what about ixquick, duckduck go, qwant, or any other or more specific/preferred web search engines)
- in case you add the possibility to add arbitrary number of SE, an other drawback (apart from the time it could take to make the search, but this should be secondary for me) should be the way the results are displayed : 'step-by-step' or 'mixed mode' doesn't make a lot of sense for me. I can believe that defining what is 'best' results is hard but at least could it be possible to use webrank like, keywords matching or something that can sort results in a more 'mixed' relevant way? but maybe there is no simple other way.
As for me, the goal of using multiple SE is to help finding pages that should be hard to find with only one SE, either because these pages are not well known, visited, advertised (thus, they won't appear in major SE)... or because it is (deliberately) not displayed in a particular SE but could be in an other. But let say for example, only the 10th SE have the correct result, even as first result, I won't see it in the first displayed results, which is not related to the relevance of my searched keywords. (don't know if I'm clear... :-) )
- one suggestion: add a 'multi-site' option: that is, in google I use the syntax
"keywords (site:site1.com) OR (site:site2.com) OR (site:..."
but total length of characters and number of site operators are limited (I have to split the query and make multiple requests). But if this could be automated and combined with multi-websearch, that should be very nice!
- and add at least one kind of dark stylish style! :-)
- last suggestion (in a more or less distant future!), don't know if it's a good idea or even if it is possible : 'normalize' (translate in unique box of options or common keywords) google hacks, duck's bangs, etc... custom options/operators to be able to use advanced search options in a unique and simplier request (by date, by type, intitle, etc...). But as not all SE are supporting all possible advanced options, that one could be tricky!
I guess it makes a lot of expectations! perhaps because their is no reliable solution at the moment for what I'm looking for and also because 'market' oriented search are no use for me, but the idea of having multiple SE gathered together by themes could be a good one.
I wish you success! looking for the future improvements...