Searching Prospero before you start a review could stop you duplicating work that is already in progress.
As part of an enquiry at work, I was searching Prospero for reviews to include in a review of reviews (an "umbrella review"). Searching Prospero would locate reviews in progress, and would identify published reviews (alongside those identified using Medline and other databases).
I have not found any search help specific to Prospero. I am fairly sure the search help at http://www.crd.york.ac.uk/crdweb/GuideToSearching.asp applies to the other CRD databases.
The References and Resources section contains a lot of useful information, including reviews of progress, and there are some interesting articles about Prospero under "Registering a systematic review", but the main emphasis of all the material seems to be about registration, not searching. So, I thought it might be useful to "publish" my notes about searching Prospero.
Complex search strategies are difficult. You can't see a search history, and so can only submit one query at a time. If you use one search box, you can't use Boolean operators, although you can use * to truncate. You can't enter phrases in inverted commas, but I wonder if phrase searching is the default. Using more than one search box does give you a way to search using Boolean in one field (change the drop down box at the top) or across fields, but you have to have just AND or OR.
You can't export results, only view them, so reviewing results for items to include in your research would need to be done on screen, and I am not sure how you would then put those items into reference management software for retention.
You can display all published records, and doing so shows that at the moment there are 5739 records, so the dataset is a lot smaller than something like Medline, and this combined with the fact that searching Prospero would be to augment more systematic searches done elsewhere, means that broader searches are still practical.