With bridging, in my case I found convenience more of a factor than the underlying rate.
If you anticipate that the bridging period will be short (and of course there can be no guarantee of that because your buyer could still walk), then I wouldn't lose sleep over rates.
I took bridging with my new mort. provider because they already had all my documentation and so it was a matter of a phonecall, one signature and 3 elapsed days to get it organised. I did pay more than mortgage rates (can't remember exactly), but with the total interest bill being 200 - 300 euro, it was well worth it for the convenience.