You are welcome, relating your question about how safe the iframe is and is it easyly blocked, well, firrst of all only to say that i'm not an expert in security, saying that in my opinion it is safe enough because you control it and i don't know if you can block it as you can do with Javascript, images or CSS, so, in the following week i will try to search about it if i have some spare time, sorry.
I don't think that your site will look less trustworthy if you decide to use iframes in yours, i know what you say about sites that use iframes to sneak malware onto your machine but as far as i know many sites with good and strong reputation use iframes very well, two sites that i know that uses iframes are GMail and Hotmail and both of them are very trustworthy.
For more information try the following
Google search about Iframe Security. After performing this search i found an excellent page named
The Spanner - Iframes security summary that summarizes in a very simple way why Iframes are considered a security risk.
But, as i say before, if you decide to use iframes in your site in the correct way and dont try to perform any ilegal activity use it.
Best regards,
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