Unless you're in a good 5g signal area it isn't an upgrade, just a change in supplier from ee to Vodafone. The ee speed on vm at best was about 70mb/s on the 4g+, generally you won't get those speeds yet with Vodafone on 4g. I'm getting about 20mb/s which is average fair Vodafone nationally. What you're actually getting on vm with Vodafone is a better indoor signal as their 800mhz is included whereas the 900mhz ee signal wasn't before.
I'm not interested in 5gb yet, give it at least another year. For example where I live not far from Nottingham there isn't 5g on Vodafone within 15 miles, that's of the city centre.
My signal has changed from ee to Vodafone this week courtesy of me changing plan. The 4g signal where I live is better than before. It's similar to ee in some other areas. The only thing missing with my 4g phone is volte. Mind you my plan update date is a few days away, so volte could appear then.