1. Comparing Samsung S21 5G and Samsung S21 Plus 5G
Essentially, the Samsung S21 Plus 5G is slightly more high-end compared to the Samsung S21 5G. Below is a comparison table of the basic specifications between these two phone models.

Similarities:
The Samsung S21 5G and S21 Plus 5G models have almost no difference in configuration. Externally, both models have a similar design with a straight-line cluster of 3 cameras at the top corner, seemingly integrated with the phone frame, creating a prominent overall design with high recognition.
The display quality of both phones is identical with the Infinity-O flat screen design, punch-hole, Dynamic AMOLED 2X panel, and only Full HD+ resolution (down from 2K on S20). Although the screens of S21 and S21+ have lower resolution compared to their predecessors, they compensate with a much more detailed refresh rate ranging from 48Hz to 120Hz. Moreover, the ultrasonic fingerprint sensor on the screen is also significantly improved.

The camera cluster on the Samsung S21 5G and S21+ comprises 3 rear lenses plus 1 front selfie lens. With the aforementioned camera specs, S21 and S21 Plus can zoom up to 3X and support digital zoom up to 30X, delivering high-quality images with better stability in zooming. The standout feature of Samsung S21 5G and S21+ compared to their predecessors and many other phones in general is the quality of night shots. Samsung's scene optimization now automatically activates Night Mode when it detects overly dim lighting, resulting in superb low-light photos.
In addition, the ability to record videos on the lenses with 4K 60fps quality and even 8K 24fps on the main lens.

Both versions of the Samsung S21 5G and S21 Plus 5G phones feature a high-speed processor with the Exynos 2100 chipset in international markets, including Vietnam. The power of this chip has been tested and highly rated over the Exynos 990 series on the Samsung S20 generation, placing it among the most powerful chips available today.
Differences:
The most noticeable difference between Samsung S21 5G and Samsung S21 Plus 5G is in size. S21 Plus is significantly larger than the standard S21 with a 6.7-inch S21 Plus display, whereas the S21 has a 6.2-inch screen.

Next comes the difference in finishing materials. While the Samsung S21 5G is equipped with a plastic matte back, the S21 Plus features a premium Corning Gorilla Glass Victus back, creating a more luxurious and robust appearance compared to the S21.
Lastly, there's the disparity in battery capacity with only 4000mAh on the Samsung S21 5G and a whopping 4800mAh on the Samsung S21 Plus 5G.
2. Pricing of Samsung S21 5G and Samsung S21 Plus 5G
The current price of Samsung S21 Plus is about 2 million Vietnamese dong more than the S21. The reference prices for these two phone models are:
- Samsung S21 5G 12GB/128GB variant: 14,990,000 VND.
- Samsung S21 Plus 5G 12GB/128GB variant: 16,990,000 VND
- Samsung S21 Plus 5G 12GB/256GB variant: 17,990,000 VND
3. Which One to Buy: Samsung S21 5G or Samsung S21 Plus 5G?
So, with a price difference of about 2 million, you'll get a larger phone, a bigger screen, made of premium glass, and with a bigger battery in the Samsung S21 Plus.
However, for me, spending an extra 2 million to get those things doesn't seem worth it because the Samsung S21 5G still has a sufficiently large screen and is easy to carry around, plus its plastic back provides a very good finish not inferior to the S21 Plus.
So what's your choice? Hopefully, this information will help you in choosing the phone product that suits you.