Do you recommend upgrading from iOS 6 to iOS 7 on iPhone 4?

I have an iPhone 4 which runs iOS 6.1.
Its capacity is 16 GB of which about 11 GB are used.
It's somewhat slow & sluggish.
The device is jailbroken, & jailbreak is very important for me.
I'm planning to upgrade to iOS 7 but afraid of turning my device into a turtle!
For those who have iPhone 4 & upgraded to iOS 7: Did you face any problems?
Do you recommend the upgrade?

Yes please!

I would really recommend, although I don't have iPhone 4 instead I got iPhone 5.

Let me say the possible pros of upgrading.
First up, are the apps. Most of the apps are also upgrading.
Secondly, there are certain functions that you can only use in iOS 6.x.x - jailbroken but are already available in iOS 7. As such are, block message and call, Control Center, and the likes.
Third, most apple users are already switching, and so, there are functions you can only use with peer iPhone users with the same iOS. Example is AirDrop.
Fourth, design. Apple's main concept of iOS 7. You might not like it but its colorful. This is actually your choice here.
Fifth, iOS 7 can also be jailbroken.
And there are things that you can discover that I did not.

Cons: Well, back to zero with the jailbreak.

Another thing. I guess it won't slow your unit, got a friend who has iPhone 4 and its working pretty well. Fast too.